RE - she allegedly did have cover, how did the insurance wiggle out of payment ?
* The answer to your question may be found under 1.9 GENERAL EXCLUSIONS TO CARD TRAVEL INSURANCE
We may assume that a blood test was taken on arrival at the hospital, so it is most likely point 12 that has been used as a basis for the refusal - something that unfortunately has turned out to be a regular occurrence on holiday trips in particular ...
https://www.americanexpress.com/content/dam/amex/uk/benefits/UK-Platinum-insurance-documentation-July21.pdf