I'm in such a strange situation! My classmate, whom I haven't seen for…

I'm in such a strange situation! My classmate, whom I haven't seen for over 10 years, and barely even talk to, is asking me for help with her child's homework! She sends assignments so I can help! Okay, I helped once, but now she's sending them again! I politely said that I was busy, but she keeps writing that she's free? And she sends assignments! How do you politely refuse? I don't want to help, I have enough problems as it is! I'm not obligated!