Girlfriend's Sora bike shifters too heavy for her to use comfortably, how to upgrade?

If you can spring for it, go get compressionless brake cable housing. That should improve braking measurably, since you'll find you need less action at the lever for a given level of speed retardation out of the calipers.

Use the lever travel shims too. Those come in 5mm and 10mm thicknesses. I use the 10mm shims on my 105 5700 STI levers and they help a lot.

I have the exact same problem with mine. I've got tiny hands & as someone else posted earlier, the problem is that on sora levers the pivot is really low down- meaning that from the hoods I'm braking with my ring fingers & little fingers only, or, if I want any kind of braking power, stretched fingertips in the drops. fine on the commute but long descents are pure pain- cramped hands, shoulders, neck. I also don't feel i've got enough power in the brakes to trust them if I let go too much, & have to keep one finger hooked around the lever if i'm in the drops or else stretch & fumble to find them. I've changed the blocks for swissstops, shimmed the levers, brought the biting point back as far as I dare.. and it's not good enough. 105s & a shallow drop are much comfier, so either find some way of making a compatible swap- or give in & go for the new bike (I have).

I don't get on that well with my Sora levers and I have relatively long fingers.

What I did find helped quite a bit was to back the brakes off slightly. It sounds counter intuitive but by running a slightly larger gap from pad to rim (remembering to adjust the pad position and angle if necessary) the bite point was a bit further into the lever travel so I was braking in more of a gripped position rather than having my fingers stretched out. I'd never heard of using shims to adjust the position but it sounds like a similar net result.

Don't clean the rims with GT85, clean them with vinegar. Etches them very very gently for a brilliant improvement in stopping.

For how long and how often is she riding the bike? Maybe she just needs to get get used with Sora shifters and brakes. Also, you could recommend her some arm warmups before the ride.

"We are currently looking at getting a set of in line levers added so she can brake comfortably while on the tops."

another vote for this solution - great for small hands and long descents - mrs antigee has 105's with the plastic block inserted to move levers back but rarely rides on the drops unless out with her training group 

Pretty easy to fit without removing handlebar tape and you don't need to replace outers just cut into them - I'd replace the brake cables though - downside is less room for lights on bar tops and dealing with the ignorance of people who hate practicality 

edit of course nothing to stop you replacing outers with compressionless at same time which is something I'd also favour

I second the shim suggestion. I couldn't operate the brakes without them. Plus the cables, pads and rims having TLC.
The bite point for small hands should also be two-thirds in, rather than the normal third in.
Plus, I have my shifters turned in slightly, which seems to take pressure off my shoulders. Trap pain does suggest the bike fit may not be quite right - reach too long?

Sort the cables and pads first. In my experience that should be all that's needed.

I am not sure what you mean by 'too heavy'.

My wife has sora STIs with BB7s on her cross bike and I have Sora with cantis on mine and the action sems fine on both of those bikes (Jagwire cables on her bike and no name ones provided with the shifters from Ribble on mine.)

My wife did comment about the reach being a bit much for her small hands, especially on the drops,  so I dug out an old pair of shims that I had knocking around and she seems pleased with them. Is it a reach, action, or braking performance issue that you have? Shims, better cables and better calipers (or possibly just metal backed cartridge pads) would solve each of those problems in that order.

+1 for teflon coated inner cables, my god they are incredibly smooth!

I have also had very good luck with lightly coating my gear and brake cables in teflon dry lube (designed for chains) before putting them into the outer cables (make sure all the lube dries first).

Flushing my outer cables with GT85 and using and old frayed cable to scrape out all the gunk also dramatically improved performance. N.B. I've only had to do this as my disc brakes have full outer cables and therefore the end of the cable is mounted low down and exposed to all the mud that gets on my cross bike.

Another vote for auxiliary brake levers.  Lots of power, and being on the tops helps keep your CoG back on downhills.

n+1 with hydraulic disc brakes

I had a similar problem with the sora levers. I've solved it in 2 ways. The original calipers (unbranded on a kona) were replaced with trp ones and I worked on my confidence going downhill so I didn't brake all the way. 

I also now now try to brake in the drops on long descents as this is easier. 

I agree with the better brake pads comment. Cheap pads (Tektro, Sora etc) are really very poor. I have disc brakes on my carbon bike and rim brakes on my steel winter bike. The winter bike has Swissstop Green pads and it pretty much as good as the disc bike in the rain - the pads really are VERY good.

1)I think the first thing is to make the brakes better so braking takes less lever effort.  If its a sora bike then it probably has rubbish brake pads.  Buy some better ones e.g. ultegra pads or the right kind of kool stop.  Before you put them on clean the braking surface on ethe rims with soapy water/panscrub and then solvent (or WD40 works too) which will improve braking.  You could also go for some nicer calipers if that doesn't help enough.  The other suggestion of some really good quality cables/ liners is likely to help too.  

2) She likely has little hands - if you have reach adjust on the brakes set them back so that the brakes are applied at the end of the lever throw - take care with this because you want the brakes to be fully on before the lever hits the bar, you might need to run the pads quite close to the rim to get this right.  The stuff in point 1) will help this setup too.  

3) Failing all that why not try to find some older dura ace or ultegra 9-speed shifters? 

4) You could also fit dedicated crosstop levers on the brake routing that allows her another position to brake from.  

Last point: I'm surprised that it is her traps that are hurting - is it really braking that is causing this or does the bike not fit properly!?  Make sure she is comfortable on the bike if you want to continue riding with her!

If braking is difficult then a new system would improve performance. Disc brakes with hydraulic calipers offer the best solution with little effort and good braking capacity. Modifying a bike will be an expensive exercise and it it sometimes cheaper to buy a complete bike with features required. But there is a lot of satisfaction when a successful modification has been completed

Sora are 9 speed, it's a long time since ultegra has been 9 speed so you'd have to do a lot more than change the brifters for your plan to work.  Blatant excuse for upgrade to Dura Ace anyway 

Interestingly my other half has the same issue, which coupled with non bedded in disk brakes made for an entertaining start to our first ride together on her new bike...........  Relationship still in recovery mode from that one

We are currently looking at getting a set of in line levers added so she can brake comfortably while on the tops.

I suspect its a small hands issue, rather than the tension of the levers.

I've found that on the Sora levers (and the old Tiagra style ones) the pivot point is quite low, so people with small hands have to apply a lot more pressure, as their fingers are naturally very close to the pivot point. I had this problem - could only really put the brakes on fully when in the drops.

The new Tiagra (4700 series)  have the newer style levers (i.e. ones that look like 105/Ultegra etc) with the pivots in a better place.

Likewise, the new Sora (not sure if its out yet - this one: http://microco.sm/out/V64bh) will have the newer style levers as well. It wouldn't be a straight swap if you went down this line - the cable pull is different on the newer style levers so you'd have to replace deraileurs as well.

It might be worth replacing the cable inners and outers with a quality polymer lined set from Shimano/Jagwire to see if the friction reduction makes braking easier for your gf, before you make a big investment in new STIs.

I just switched out my cables and the braking feels a lot lighter and smoother.