If she's one of those best friends that you're not getting laid with, tell her that you'd rather find a girl you're looking to fuck
if she's your best friend that you think you can get laid with, run the fuck away. . . one thing I quickly learned late in middle school/early high school is that becoming BFFs with chicks absolutely kills any chance you have of banging her and you're just delaying the inevitable heartbreak. If a chick starts telling you about her problems that's when you know you're about to cross a dangerous line and you either tune her out or ask her out.
If you really don't give a shit about what anyone here is saying and you're going to make a big scene for this bitch anyways, I honestly can't think of anything that wouldn't give me douche chills