Tell your straight friend you're a lesbian, let it sink in, allow her time to think about all her lez fantasies, THEN make your move! Guaranteed results!
Correct me if I'm wrong, but when a lesbian friend "comes out" to a "straight" friend, the "correct" thing to do is hurry to assure each other it's "perfectly okay," like the lesbian is NOT coming on to her or interested AT ALL! Has the straight fantasized about it, is she interested? Any questions? How's YOUR sex life? So lots going on just below the surface. At least sometimes (often?) sparks must fly.