Even if she is bisexual? That STILL doesn't mean she wants to be in relationship with you just because she is oriented that way. (But you really don't know, you just hope.)
If you want to KNOW something, you have to ASK.
So you could just ask if she wants to be in relationship with you. The how
of it? You could choose to do it straight up like
"I like you a lot, and would like to be in relationship with you. Would you want to explore that and be in romantic relationship with me? Would you want to set a date to discuss that possibility?"
and just get the ball rolling.