Poor Maggie and poor you. You both have our sympathies.
Our old girl Betty was exactly the same at 14 years old, and soldiered on till she was 16 1/2
Is Maggie eating the low salt diet? If yes, that's a great start.
Blindness + Deafness + dementia is a horrible combination, leaving her very isolated and disoriented. It was particularly distressing for Betty at the stage that she had partial hearing in just one ear. Once that ear went deaf too, she calmed considerably.
Things we did to help Betty, that seemed to work were:
Kept spaces she was used to living in free from new object that she could become entangled in. She would get entangled and confused under dining chairs that were out of place for example.
Let her live pretty much her normal routine, and left doors ajar in the house so that she could have free run. ( fine until pee-related problems from the kidney failure kicked in.
Sense of smell: Betty fortunately kept a good sense of smell to the end, so we were still able to play hide and seek games with her by hiding toys and treats
While going through the partial deafness phase we stopped giving her sound commands while out on our walks. She very quickly adapted. I am convinced that she retained some sort of low frequency hearing as whenever we stopped walking after a few seconds Betty would always stop too. We were able to "call " her back to us by stamping our feet.
We're lucky enough to live in a part of the world where there is loads of free space in which to roam. And roam we did, mostly with Betty off lead. Using extremely limited sight, but her still good scenting capability she very much enjoyed the freedom, and always found her way back to us by scent. We never lost her once, not even on her frequent off-piste excursions in the forests that we walk.
Touch: Betty always was happy being touched, so we made a point of fussing her often, which she liked.
Reaction: Betty was always a communicative girl, and as she grew older we made sure that we were very reactive to her. So if she got into a fix under a chair for example we'd quickly be able to untangle her. I think this is important as it lets the dog have freedom to mooch about, knowing that if they get into difficulties their slaves will come a-running:-)
OK so that's a rather long list of things that worked for us. We hope Maggie will adapt equally well.
All the best
Jon, Sarka and new-boy Barnaby.