Does anyone have any experience with overriding a power of attorney?

My aunt is the power of attorney (POA) for my grandmother. We're her last living relatives because my aunt never married and didn't have kids, and my dad died when I was little. My mom and my grandmother haven't talked since she married my stepdad 15 years ago.

My grandmother is 96 and lives in a nursing home. My aunt wants me to help her make decisions because she says it's really hard having this all fall on her. I went to a meeting at the nursing home and they asked my aunt about a DNR for my grandmother and my aunt said absolutely not. They explained that at my grandmother's age CPR would almost certainly do more harm than good, and my aunt told them that my grandmother made her wishes clear in her advanced decision document. The home told her that the document is a letter that was never notorized and never signed (It's just a typed up letter that pretty much says "let me die when it's my time") so it doesn't stand legally. My aunt said she's not making my grandmother a DNR because legally they can't do CPR or hook her up to machines because that's in her advanced living will or whatever.

I told my aunt to just sign the DNR because it's what my grandmother would have wanted and if she doesn't, they HAVE to do CPR if my grandma dies. She said no, she's not signing it. I told her what she's saying is going against my grandmother's wishes and she's using the advance will as a DNR anyway so just sign it!!!

She won't. And she wants me to make decisions but won't sign over anything to me either. Common theme. I'm trying to see if I can take over as POA because she wastes so much time just power tripping. Like she wouldn't sign for meds and pay for things because she told the home they already had all her information and the home told her that meds are supplied by an outside pharmacy and she has to fill out and sign the form from the pharmacy. She didn't, so my grandmother was without pills and the home ended up sending her to the hospital.

It's just a nightmare. Has anyone had experience with this? I'm in Hamilton, Ontario (I'm from Canada). The home gave me resources but they haven't been helpful yet.

Edit: I called an attorney and he's helping me out. In the meantime, my grandma fell and broke her hip this morning. My aunt is refusing to give her ANYTHING for the pain because she's never had pain in her life and she says "Of course she has pain. She broke her hip. Wouldn't you be in pain? You just want to dope her up and I'm not having it!"

I'm trying to get emergency guardianship because this is cruel and my grandmother is in agony. My aunt won't consent to pain medication though.