How to handle a decreased ability to engage with the world?

Hi!
The backstory to save time later:
My husband and I (and to some extent, his younger brother) are the primary caregivers for his almost 87 year old mother.
She still lives on her own, makes all her own decisions, etc. The younger brother lives in the basement, but sadly doesn't engage more than he needs to.
So, my husband and I spend more time with her, help her with things she needs, etc. And she's a LOVELY human... I really lucked out in the mother-in-law area.
She never had a very big world. She was a stay-at-home mom, and, from what I've learned over the years, a very traditional and somewhat submissive wife to her husbands (my husband's father, and then a second husband - both long dead). Even once the kids were grown she pretty much took care of her husband/the house, babysat her grands every day, and knitted, She went out once/week to bowl, grocery shop, and go to the bank if banking needed to be done. That was pretty much her life.
And when the bowling league left the area, her world got smaller. And when she surrendered her keys, it got smaller again (not in where she WOULD go, but in that she COULD go on her own if she wanted to).
She patently refused to learn to use tech, so her world is even smaller. I handle anything she needs (making deposits to her bank accounts, paying bills online, etc) because she doesn't want to go in person, and I honestly don't want to have to schlep her around for things I can do online.
Now, she really doesn't want to go anywhere out unless she has to. Her life outside the house includes doc visits and bi-monthly pedicures to keep her feet healthy. She won't go out to lunch or dinner. She won't take a day trip with us. She really just wants to sit and watch TV, and engage with people if/when they visit her.
And all of that is what it is, but here's the question I need help with.
She wears hearing aids, but they don't seem especially good, and that's even more true when she has to talk on the phone. She won't consider getting better ones. But that means she has a hard time on calls. Speaker phones are worse for her.
Recently, one of her CD matured. She needed to talk to the bank to figure out what she wanted to do with the money. That was something we could do by phone, so I went over to her house to facilitate that.
I called the bank, and Elton asked to talk to Mom to make sure he could talk to me. All he asked her was her name and her birth date, but she clearly had a hard time understanding him. All of this was harder for her, too, because he had an accent.
We got through it, but I can see the day coming when even doing that will be impossible for her.
Do any of you have experience with this?
Whether it's the bank, or the county, or Social Security, or anything else, what's the best way to navigate helping her communicate when she is the one in charge of her own life?
One more note - her life is well set up legally. My husband has limited power, and could do things like talk to the bank, but she doesn't want him to, because she wants to do it.
And as small as her life is, I really don't want to make it smaller if I can figure out how not to.
Thanks for anything you can share that's helpful.