My hubby’s ex wife wants money. How do divorce agreements work?

My husband is amazing. He was married twice before me. His first wife he was married to for 12 years and divorced is suing him. Part of their divorce agreement was he was supposed to pay her $250,000 but after paying $150,000, she wrote to him saying she wasn’t going to enforce the agreement. It’s now been over 9 years and now she got a lawyer. We have four kids and I’m worried she’s going to get money from him. Anyone know how divorce works? Can an ex say they won’t enforce something and several years come back and do it? They never had kids. But she also opened up credit cards in his name and ended having him pay $60,000 to fix his credit. She was trying surrogate.

Any help will be appreciated.