I've never known this illness to affect females only, i have not had this problem for along time know, when i was starting out i lost many batches of fry to it, have never lost adult guppys. My suggestion get them in a little planted tank, as there tails are pointed and there anal fins are clamped they start finding it hard to swim, so without males stressing them and not being to far from food, they should have a better chance at survival. I suggest livefood, pack the tank full of it, Daphny and Mossy.
Shae