Bisexuality Support Group
Bisexuality is a sexual orientation which refers to the aesthetic, romantic, and/or sexual attraction of individuals to other individuals of both their own and the opposite gender or sex. Most bisexuals are not equally attracted to men and women, and may even shift between states of finding either sex exclusively attractive over the course of time.
At the same time though, I have a question for you, what would you want if you were in her shoes?
Someone else may feel differently but I don't see how you can be a good friend, and or care about her and not tell her. If you know that she would not do certain things if she knew, then you need to tell her so she can stop doing those things.
Yes, you are taking the chance of losing her, but do you really want to do her wrong? There is a chance that she will understand and not leave. That's my two cents.