Give her forewarning. Say if you want to leave in ten minutes time, tell her that she needs to wrap up and that you are bringing her to xxxx or you are going to do xxx with her and that she has five more minutes to wrap up.
1. Give her a target time to leave
2. And something else to look forward to
Of course she can\'t read the clock so if she takes more than five minutes to finish you still have buffer time for yourself.