If she is there for you when you need her, that is all that should matter to you. You are not her mother to judge her for her sexual life.

I have no female friends whatsoever. I moved to US 8 years ago, and still haven't managed to even meet any women my age, so I am dependant on my sister-in-law and her best friend for a female companionship. Needles to say I have nobody to talk to when I have an argument with my husband, because they're both biased. My only female friend from my country lives in Kuwait, so she can't be with me when I need her.

I'd give anything to have just one female friend who can be there for me when I need to cry, listen to my bitching, get drunk with, paint my nails, and eat a pound of chocolate when depressed. You have all that, and you're letting your judgement get the best of you. Please don't do it, don't lose your friend, because one day you might end up being alone and needing her.