My brother various times has complained about his health and especially his dental health. He’d diagnose himself, but always throw up some obstacle like cost or having to go to a very specific doctor who he’s researched online etc. My sister eventually called his bluffs and set appointments for him and drove him there etc. The shame of not coming to a set appointment seemed to motivate him for some reason, so he’d relent.
We were shocked when he finally relented to go to the dentist and they ended up pulling most of his teeth. We had assumed he was delusional about how bad his teeth were. His explanation was he was embarrassed that he let his teeth get so bad. He had some fantasy of getting all his teeth pulled and implants on a trip to Costa Rica. My sister had offered to pay for implants, but he won’t quit smoking and they won’t do them.
Generally we set everything up for him and say he’s going and that’s that. For a while he got sort of hooked on acupuncture and we’d take him periodically, but eventually that faded. The only doctor we can’t seem to get him to see is a psychiatrist— none are good enough or competent enough for his unique and special brain chemistry, blah blah blah blah… He has bipolar disorder, but the behavior is fairly typical. I have SZA, and have had similar anxiety seeing doctors and such, but had a psychiatrist who wouldn’t see me if I didn’t see a doctor regularly, so I got in the habit.
My advice would be to play off of fears, delusions, vanities, duties or shame to coerce her to go. Straightforward logic will likely not work, I think you are better off with an emotional argument. This is not a rational matter, so don’t treat it that way. Good luck!