Women are sexy, even to another woman.
Just becasue she dances or even kisses another women does not make her bi.
Group sex may not be her bag of tea, maybe the thought of many people or another hairy man sickens her.
She may be intrested in the soft body of a woman maybe a threesome at most.
You want to aproach the subject sober (plenty of time for drinking when u get the ladies alone) And communicate with her how you feel, how her interaction with other women makes you feel. Ask how she feels about it, and if she has had some possible fantasies or curiousity becasue you have some.
Dont ask anyone to go out on a limb, its too scarry. Go out first then reach your hand and let them know its safe. You'll get further that way.