Don't pay it. (trust me, I speak from experience) The type of person she is, you could pay it and she could leave you anyway. If that's what she chooses to do, let her leave. I know it's a lot of income, but there is no guarantee it'll be there even if you do pay her daycare. Besides, maybe some little one with a responsible mommy is searching for the right daycare right now and could use the opening.
I used to panic when children left the daycare for whatever reason, but they were always replaced quicker than I would have believed.