No question or concern is "trivial" on here brightonbelle. If it is worrying you then its important.
I take it that your mum hasnt been in a CH long? It can take several weeks for someone to settle. Going in other rooms is common in CHs, Im afraid. Mum has a tendency to find a bed and sleep on it - doesnt matter whose it is
She also gets up at all times during the night and wanders around. Its par for the course with dementia and the carers should be able to deal with it. From the way they are trying to encourage doll therapy it sound like they know what they are doing.
It also takes a while for reletives to adjust too - you are in the early stages of this step and are probably feeling anxious and guilty. My mum has thrived in her CH. She is settled and so much less anxious. I think the effort of trying to live in her home was driving the paranoia and it was a nightmare. She is now content, has put on some weight and made some friends.
It will get better.