Do I save up the money to give her a refund?

I've been a babysitter now for 4 years, and I have really great kids and parents. All I ask is that everyone is on time for drop offs and pick ups and that payment is made before the 5th of each month (full time $400 amonth, includes breakfast,lunch, and snacks). All parents have to sign my agreement application before I watch their child, just so we are all on the same page. In the agreement no deductions of any funds for sick days, personal absences, personal vacations, and holidays are permitted. Once I receive the funds they are immediately used for bills, food and babysitting necesseities. I have a friend of mine who for some reason of her own kept her daughter home for most of the entire month of August. Now, she's asking for a free month for September. I can't afford to do that. I'll be short of bills etc. Exactly why i made the agreement that she signed. What would you babysitters do out there? I saw on Judge Judy once the same thing happend to another sitter, and the judge was for the babysitter, she says cause day care was open for service, and she chose for reasons of her own not to bring the child, but still, i feel saddend, and confused. Help. Should I just save up the money to give her a refund. She's threatening not to bring her daughter back.