How do I explain to my elderly mother why we can’t leave her home alone?

I can understand her point. She doesn't think she has a problem, but YOU know that she does.

SO... don't introduce the person as her 'sitter'! Just say you have a friend that needs to stay with you while her home is being fixed.. (whatever) and she will be here while the workers are in her house!

Introduce the person as a FRIEND.

Mom -she really doesn't want a sitter

Who are you trying to explain this to?