Circlenet is very inexpensive and I don't think you have to use their voicemail.
There are several ways to use GV. I don't know if any will work for your mother.
You can route all inbound calls to the Auto Attendant. After the AA answers, the call will not go to GV voicemail. Change the AA prompt to say something like:
"Please press 1 to reach Mrs. Pasta514"
You will also need to make changes to prevent callers from making a new call.
You can get her a cordless phone, so she can carry it with her.
If you have an old Android cell, calls can be routed to it. You don't need a cell calling plan, just install an SIP softphone on it.
Does her phone have a built-in answering machine?