Honestly OP, the parallels between my life and yours are uncanny!
My DM has just had her second cataract operation a few days ago. She had her first eye done in August.
My DM has also just been diagnosed with mixed type dementia, she has been in hospital for heart conditions in the last year, and she also lives with me! As I say, uncanny!
Also, my DM had refused to have her cataracts fixed for about three years. She was absolutely adamant. I think what persuaded her in the end was the fact that the glasses were barely making a difference any more. She thought it was deteriorating vision, and thought stronger glasses would help, but actually it was the fogginess of the cataract that was impairing her vision.
She was SO nervous. Really, really nervous.
Also, my DM has cerebral palsy and can't relax her body. She also tends to jump quite badly if she hears a loud noise. Because of these two things, she was absolutely terrified that she'd jump during the procedure and that there would be a terrible mishap. It was absolutely fine. We asked about a sedative and the surgeon said he preferred not to give it - he said that if she were a bit sleepy/drowsy, she might be even more startled at a loud noise or she might suddenly realise where she was and startle.
We didn't call it an operation. We used the phrase "procedure" as it didn't seem quite as big and scary.
The surgeon carried out 28 cataract procedures on the day we were there this week. He does between 15 and 28 cataract procedures every day. It's just like a production line, it's SO fast.
Does your DM think that both eyes will be done at once? If so, she may be panicking that she won't be able to see. I find with my DM sometimes I need to point out the obvious things, especially now. So could you reassure your DM that they'll only do the one eye at once and that it won't make it worse than it is now? The improvement is virtually immediate. Could you get her excited about TV shows she could watch once her eyes are done - get her looking forward to what she could enjoy again?
I told my DM that the things she was worried about was the same things that everyone else worries about when they're having their cataracts done. That they do thousands of these ops every year, and they are a really basic procedure. A nurse held my DM's hand throughout the procedure. She was in there for literally about 10 minutes - I didn't even have time to finish sending my message to my friend!
I told my DM about this great series of books and she bought them - as soon as her eye has properly healed, she'll be getting new glasses and will be reading the books. She can't wait! Would something like that help motivate your DM?
Failing that, what about the opposite - if she doesn't get them fixed, she could lose her sight almost entirely?
Also, have you reassured her that you'll take her and be with her up to the procedure and then immediately after? It may be obvious but I find my DM benefits from me actually spelling things out a bit more.
Sorry for the long post, it's just that I've been through exactly what you're going through now - it took us a long time to convince DM but she's really glad that she did it. Would it be possible for your DM to speak directly to someone who had it who can tell her firsthand how simple it is, and how revolutionary the outcome was?