POA never visits. POA took mail key, I can't send mail. POA took cell phone. I'm in TN my mother and I are really close. In 2017 I cared for both my parents with Alzheimer's before my sister poa forced them out of house to sell to her daughter. Nothing has been in the best interest of my mother and now my father is deceased.
With Alzheimer's a cellphone can become overwhelming to use. Heck, it is overwhelming for me to use :P Give me landlines any day. And with the mailbox key, I wouldn't be surprised if your Mom was misplacing it.
The Assisted Living/Memory Care facility where my Dad lived didn't have separate mailboxes for that building. Mail was delivered directly by the Staff to the resident. Therefore, you can still send mail to your Mom.
There comes a time when some parents who have Alzheimer's need to have a village looking after them, thus the reason why your sister decided that was in your Mom's best interest. And the selling of the house, no matter if it was a stranger or a family member, the equity is helping pay for the Assisted Living care.
Have you visited with your Mom lately? Or has it been awhile? When it comes to memory issues, it can advance quickly. It did for my own Mom.
Side note, I have POA over my mom (along with my brother). Mom had to sell her house, no choice about it. My son bought it at FULL market value & the money from it is what is paying for her care. Unless your sister gave her daughter a price break on the house, or is “hiding” the money, there is nothing wrong. If she did give her a price break, and Mom needs Medicaid, your sister will be paying it back!