Is there anything on the market that fits the description below?

The thing with the computer, no. I mean yes, it is possible. But it would be expensive. It would be cheaper to pay for internet. I know it's 80 a month, but that's the cheapest way to go for computers.

There are phones with volume boosts, but they're hard to find. I had the same problem and found an old land line phone in a resale shop. Works great.

There are also devices for the death or hard of hearing.

Addition.

If your really stuck on doing it with the computer and not the internet. You could go searching for old hardware. We use to do something like that in the 80's, through the phone line. But I don't know where you'd find the hard ware. Or even the software.

Do a little research on telephone devices for the deaf. There are several devices some of which will be provided by your phone company of a third party without cost. A large number of 94 years olds are also visually impaired so many of the devices for the deaf use monitors with extra large text.

Can't involve the internet? That's a pretty big restriction these days. I suggest teletext devices (TTY). Besides, with TTY she can communicate with emergency services.

EVERY internet capable device fits that description. EVERY device of that type DOES use the internet. You can't even place a call from a landline phone to another landline phone without using the internet these days. The ONLY exception is if there is a DIRECT wire from one device to the other. While that is possible, it is ONLY available as a custom item.

There are many things. One is TTY/TTD technology, which has been around for at least 30 years, probably a lot longer. Another is e-mail.

It sounds like the only electronic connection you have is by telephone. Use a Teletype machine or something similar. Once upon a time, that was how you communicated with a computer in another place. Find a retired computer guy who remembers such things to help you out.

Textphones do that.

A TTY or TDD device using landline phones is designed exactly for this.

depending where you are there are phones made for the deaf. what the deaf person sees is the words on the phone screen

Direct phone line with modems would work. Phone companies have text phones which have keyboard. Try looking at the RNID website. text phones are giving way to Next Generation Text, but you need the Internet for that.

If you can get mobile phone coverage you can send data via that. You just connect your computer and continue to use that.