It'll probably be the seat. I suffer from a slightly different thing where my groin goes completely numb after about an hour (if I don't stand up regularly), but the reason behind it is basically the same, pressure on either nerves or blood flow.
First thing to try is riding with the seat tilted different to how she has it currently. For me (specifically on the turbo trainer) it was to tilt the seat down (at the front) a reasonable amount. The negative to this is that I always feel like I'm slipping off the front of the seat. If tilting the seat doesn't work, she may want to try different seats. There are many different shapes which can alleviate pressure on certain parts.
That's assuming that she's been setup on he bike properly (seat height, front / back). There are plenty of guides on how to do that online.
As for where to buy this stuff. Wiggle. You can look at the ratings people have given the gear, and in the UK at least they're easily one of the cheapest stores.