I've had "passes" made at me, too....friends (but not "best" friend)...and co-workers who were bi......I just ignored them! And avoided them.
It actually made me angry. As I'm straight also, never had the desire to be Bi or experiment.
Since she is "ur best friend"....it's gonna be a lot harder to ignore or avoid....if talking to her doesn't work, and she continues her behavior, you may have to take a drastic measure and cut her off for awhile!
Sounds as if she's confused!....And I bet it makes you "feel bad". But remmy, she put you in a bad position!...She needs to apolize....and leave you alone....if she won't....then it's up to you to continue to be her "best friend" but knowing her feelings toward you!....As for me, I would "cut her loose".