My sister went behind my back and got power of attorney. My mom might not have known exactly what was going on. What do I do?

A power of attorney can be contested by a third party (you in this case) and should be if you feel your mother may have been confused OR if you feel your sister is operating dishonestly, such as moving all your mothers belongings to her house and putting your mother in a home under false? pretenses. Make a list of abuses you suspect (which can include witness statements, say from a neighbor, doctor or bank official) and file a petition with the district court in the jurisdiction of your mothers address. You have every right to do that if you feel something isn’t right. You can also submit a discovery request for financial or other records to make sure your sister isn’t acting illegally. As a power of attorney, your sister must act in the best interest of the principal. My advice is don’t wait if something feels off. Good luck!

You don't seem completely certain of your mom's capacity to understand what she did, so it's possible she might have understood. Your mom is free to appoint anyone she wants as her PoA IF she comprehends what she's doing. I would consult an attorney that specializes in elder law and get some advice before moving forward. To contest the PoA, you'd have to prove your mom's incapacity. You'd have to get permission from your sister to get her tested. What are the odds of that? Would your sister show you the PoA docs so you can make sure they have been correctly notarized (with 2 witnesses, etc)? Do you suspect financial (or any other) abuse or neglect? Last resort I think is seeking guardianship through the courts and if the court doesn't like how things are playing out between you 2 sisters, it might decide to get the guardianship instead. How sad things have to be like this for our mom...good luck!