How often do big insurance companies (IMG(Patriot), Atlas) pay out genuine claims for visitors to the US?

My mum has 1 pre existing condition (hypertension) for a number of years and it is stable with her medication. She also takes preventive medication for cholesterol (a statin). She’s also very overweight. We have a family history of heart disease, but she hasn’t had any problems so far and no diagnoses from the doctor either. She tends to be very healthy overall, rarely requiring to see the doctor. She doesn’t anticipate anything bad to happen in terms of her heart health and her doctor has given no indications that she should worry.

She’s travelling to the US, and I want to purchase either Atlas’s Visitor Coverage (90 days, emergency cover, acute pre existing cover), Patriot’s visitor plan that covers pre existing conditions (without the acute onset limitation) or INF/Hop’s Travel assistance plan that covers pre-existing conditions completely BUT isn’t an insurance plan. I mostly want my mum covered for unforeseen accidents (whether she falls and breaks something OR something like a road accident) and injuries that require emergency care.

Personally I’d prefer if my mom has the best coverage for the rare chance she has a heart attack/stroke/any complication related to hypertension, but after reading reviews we came to the conclusion that most insurance companies do whatever they can to deny claims (and go as far as having bad call centres, responding too slowly, taking months on paperwork that should otherwise be quick).

Here’s the question I have: If we get the atlas plan with acute onset emergency cover, and she has a car accident, do insurance companies find a way to tie those things back to her pre-existing condition (hypertension) even if it has nothing to do with it, making the plan redundant for someone with a pre-existing condition, even if in reality the emergency doesn’t have anything to do with the pre-existing condition?