How do I find out if I'm still the power of attorney for my ex mother-in-law?

Can you ask your ex? If it turns out you are then maybe she forgot and would prefer someone else. She needs to do this before she legally cannot.

You don't have to do it. You can resign and let her know you are resigning.

Your her POA until she revokes you. This is something you need to find out. If she is in her right mind, ask her to revoke you and assign someone else if you do not want the assignment any longer. Me personally, would never be a POA for my MIL. I had my Moms and now have my nephews. At 76 I am tired of being responsible for people.

Are you asking because you want to be, or because you’re afraid you’re going to be asked to make decisions and manage her affairs? Since I assume you’re not currently acting on her behalf and managing anything for her you can just say “no” if someone calls you up and asks you to make medical decisions or manage her financial affairs. If she has you in her paperwork it doesn’t obligate you.

If you’re worried she has ONLY you in her paperwork and she’s going be stuck with no POA you could reach out and say you were thinking about it and you wanted to make sure she didn’t forget to change things when you divorced her son?