My question involves child support in the State of: California

I am the CP and the father. My ex (ncp) lives out of state and was ordered to pay 103 a month in CS. She has not paid in over 4 years (not seen daughter in 5 years). She states that she is mentally unstable and cannot work. She had a doctor from the state she lives in say that she is under his care and cannot work. The Judge put her at 0 per month because of this. Is this legal? All she has is a doctors note. She is not on any type of state disability or SSI. And here's the kicker, she's had 2 children since being ordered to pay CS and takes care of them. Guess she'e mentally stable enough to take care of those kids.