We cannot agree on where our senior relative should live. Is there a service or court that can determine her best intetest?

Has the GM who was taken by the granddaughter been diagnosed with dementia? If not, she has a right to choose where she lives and the GD has no authority to remove it, POA notwithstanding.

I think I'd bring her back to her home, take her to an estate planning attorney and execute a new DPOA removing the granddaughter.

It would help though if you explained who "we" are. What relation are you, and what is your interest?

So can you give us more information about why the granddaughter removed her grandmother from the living arrangement? Was she concerned about conditions or what?

And are you trying to figure out where to put the other sister, or are you still wanting the sister who was removed returned? Please tell us more, so we can give you better answers.

I don't know of any service or court who will mandate where someone lives.

The granddaughter was asked to help out on the weekends and help pay for weekend support service when she was not available. She has POA. We want the sisters to remain together.
When the emotional wellbeing is not being consideted, there must be something that can be done.

Does the granddaughter have DPOA, and does she have it over one sister, or both sisters? If only one then she cannot decide where the other lives.