First off, sorry to hear that she's short-changing you! Don't blame all teachers - I have amazing teacher families, and come from parents who were teachers, and married one! lol

Secondly, I have in my manual, you don't pay on time or proper fees, you're dinged with late fees of $20/day plus the weeks pay.

I do agree with Mimi on the fact that she should pay in advance.
I had a family with 2 school-aged children that came two days/week every second week (if they even came at all!). They had to pay on the first day of the month (monthly fees) for the month.

Because this woman only has her child in your care 2/days/week, then I would do just that! It's not a lot to fork over....

Question for you: Did you have this woman sign a contract? This will also cover your ass and help you demand the money and RESPECT you deserve. If she can't get rolling with your rules, I would definitely term them, and accept a family who will respect you!

Good luck!