Thanks for all your help.
It is caused by yeast, so make sure all towels, underwear, socks, sheets are washed in hot water, Make sure everything gets dried thoroughtly. Tide and baking soda. She can take Diflucan or use a cream. She needs to take a probiotic to balance her flora. Women's systems are delicate and it can be hard to get it right. She may need to cut way back on sugar.
All women get them more so when they are younger. Go to walgreens to the female part and the have med. For it if it does not go away then go 2 the doc
This is unlikely to be caused by you. A yeast infection occurs when any single bacteria in the natural vaginal flora overgrows. Does she douche? If she does, she needs to stop. If she doesn't, it's worth researching things that can lead to this sort of environment and make sure she doesn't do any of those.