I pay until she offers to pay. When she offers to pay, try to play it off by saying "no, it's ok I've got it," the first time, then if she insists further, then let her. If she lets you pay without following through with her request to pay (ie, after you say 'no ive got it' she doesn't give another attempt to pay), when the check arrives jokingly say (add a bit of laughter with this), 'I'll let you get the next one" as you look at the check with a slightly grimaced face. Usually, she'll pick up the check after that one or, if not, the one after that.