If your mother is setting DND or any other focus mode that is blocking your ability to contact her you should first delete all the focus modes. DND can’t be deleted, but you can set it up so that even if she accidentally enables it you are allowed to get through.

As for other settings you could try and see if ‘Screen Time’ can be used to create some restrictions. Also you may consider deleting apps, even default Apple apps, that your mom doesn’t need to simplify things for her.