babysitting conflict!

Erica
So I have been watching two buys for a fellow army wife. I only get paid 35 a day, which is not a problem, I'm really just filling some time during the day. But here is my problem, she is super flaky! She never knows when she will pick up her boys and if she does she's usually two + hours later than what she said. Them she forgets to pay me. 
Right now she is two and a half hours late and owes me 140 for this last week of watching them. What do I do?
I'm super frustrated!
Oh and to top it off her oldest is super spoiled and screams at the tip top of his lungs if he doesn't get his way, so he's constantly screaming!