There is a reason why 99% of the time, when a girl says "Let's be friends", in your mind you should be thinking how great it'll be to never talk to them again. Typically, when they say "Let's be friends" and the mean it, they want another girlfriend. Tried it before, it pissed me off, so I quit.
I believe in clean breaks most of the time. If I've gone out with someone, and I wasn't interested in them as a "friend", but perhaps for some other reason
, I'm not interested at all in being a friend.
This girl is having regrets about the whole breakup thing. She's coming off as pretty immature and somewhat in denial about it. If you tell it like it is, be prepared for the tears to start coming from her. Maybe that's what you need to do -- just tell her what's going on. That you're really not interested in being friends, that she gets on your last nerve, etc.