My ex wife's mother has cancer
How do I help someone I don't want to get close to when they need help the most? My ex wife basically used me like a rag doll and threw me away when she was finished. Now I clearly see she needs support, but knowing her and her situation; it's going to get emotional and I'm still not completely over gaffe.
Contact your MIL directly and ask her what you can do to help her at this time.
No need to involve your ex in any of this discussion.