Sister is using Mom's credit for cell phones, internet and a credit card she owes. Any advice?

I meant to say this:
As far as the POA goes and if you used your state's standard form, it might NOT even allow for multiple people to be on it.

And, as I re-read my answer, I guess you can tell I've gone through something similar and maybe answering in a somewhat emotional manner. :-)

Getting a lawyer might be helpful. My family had some issues so I got my mom a lawyer. She doesn't have a lot of money so I'm careful not to use much of his time. However, every once in awhile, I will e-mail him my list of questions. He tells me which legal things I can and should do as my Mom's POA. If something looks shady, I collect these things and e-mail him my questions, every once in awhile. If it needs a discussion, we often do a short phone call.

As far as the POA goes and if you used your state's standard form, it might even allow for multiple people to be on it. I had POA for my mom in her original state, and it specifically said only one person could be on it. Now, she's moved in with me in another state, and I don't think our current state's POA form restricts it, specifically.

But here is my point on the POA and I know you know this, but let's just state this here for the sake of discussion: you and your sister could not possibly do the POA in a joint manner. I think it's pretty clear that that's not going to work out. Your point to your mother is to keep reminding her that you're doing your best and that you need to know if there's any reason she's not happy with your work that she'd change the POA. If she says anything about feeling sorry for your sister and adding her to the POA, just point blank tell her your mother that, if she does that, that you're gone - that you can't see that working and that you're not going to sign a new document, yourself. and that she'd be on her own with your sister. Tell her that, if she's been unhappy with our work and wants to switch to your sister that she's welcome to do it.

You, as POA are responsible for finances as well as care. If she did these things without your mother knowing, you report it as a crime. Otherwise it falls on you for not reporting it.

Cancel your mother's credit cards and have them reissued in her name only. I read a few days ago of a cellular carrier which paid termination fees if the service was transferred to them. So cancel your sister's service and transfer either your mother's or your service. You'll have to do some research as I don't recall which carrier it was that made this offer.

If your mother is paying for your sister's internet service, cancel that as well.

Explain to your mother why this needs to be done though.

I don't know how you could sue her unless she fraudulently used your mother's credit to obtain the services she's abused. It sounds like your mother agreed as I don't see how your sister could be using your mother's credit card otherwise, even with the fast swipe features. Does your mother still get the bills, and is she paying them for your sister?

Does your mother live alone? Does she experience forgetfulness and/or show signs of cognitive dysfunction? If no one's living with her, your sister could easily manipulate your mother into co-signing for additional debt. I don't know how to address this issue, especially since nothing has been written about your mother's status.

How is your sister threatening your mother to manipulate her into responsibility for financial misdeeds? And how did she "manage to get on" a will and threaten the Personal Representative (as they're designated now)?