Can daughter in law be held responsible for care of mother in law?

So what do you mean by responsible. Are you afraid that if something happens to ur husband you will have to take on the responsibility? I would say no. The surviving child would need to take responsibility for mother. Not meaning she/he has to physically care for them but make arrangements for Moms care. Unless you are very close to MIL I would not get a POA. No way would I have wanted to care for my MIL. She could be nasty and stubborn when she wanted.

If you want to be then yes. I think it depends on your relationship with her. When it comes to your own blood family, I can see where that guilt to ensure they have the proper care can come from, but in-laws are different, especially if she was not nice to you.

I think we need more details, can you please provide and then I will circle back to this?

Only if she wants to be. Seriously. If your the daughter in law and Regina is your mother in law, no one can force you to be responsible for her, unless you allow them to. If you want to be responsible then MIL/Regina can assign you POA and give you that authority.