Yes, we've already done this. The problem is that of the 12 bikes we've been given, only 4 of them are small, and the remaining 8 are too big for most of the participants. Even the smallest bikes are a bit too tall for the smallest women to be able to put both feet flat on the ground.
Two women have actually brought childrens mtb-style bikes, and have had success with them. The problem with them again is that the bars are quite low, but for some having a small bike was the key. I'll have to ask if they would consider lending them around, but I hesitate to ask when they've only just cracked the code themselves :-)
2 of us instructors have brought altogether 4 of our own bikes, but for beginners a regular size mtb without a low step-in frame is quite daunting. The most experienced ones have had fun riding them, though.
Winter riding is much less about badassery and much more about bundle-uppery. - malkin
1995 Kona Cinder Cone commuterFrankenbike/Selle Italia SLR Lady Gel Flow
2008 white Nakamura Summit Custom mtb/Terry Falcon X
2000 Schwinn Fastback Comp road bike/Specialized Jett