I think you are going to have to take the bull by the horns and just tell her. If she has failed to take a hint, I don't see what else you can do other than stop seeing her and you don't really want that. Try making a joke of it first, to see if that works. If not, tell her straight.
I work with someone like that and she drives me nuts, I couldn't get a word in edgeways even if I wanted to as she never pauses for breath! I just yell at her now, 'For goodness sake, SHUT UP!!!' and still she jabbers on and on about who knows what.