Bro, the way i see it is this, unless she knows right from the start you are a sexual being, u will already be in the friend zone. If so, its too late, chances are she will not want things to change. In any case dont let it be her who LJBF's you. Try a jealousy plotline, get her emotions going, let her realise she craves you. Let her come to you, that way your not been creepy or anything (by becoming sexual all of a sudden), if not, embrace her friendship, no one lay is ever that important to lose out on that, besides think of all the hot bitches she could introduce you to - moreover, if you create and maintain an instant sexual frame with them, again this may have potential for a jealousy plotline, she will be like what the fuck where did you come from, she will feel like the one who has been LJBFs, and she may well realise she does infact want your dick in and around her mouth
hope this helps boss!