Hard to believe! My father has both medical card and health insurance. Only way that could be an issue is if its means tested medical card and she is on low income, someone might wonder how she could afford insurance but if all above board then no issue
" Q. I have a medical card. May I also hold private health insurance?
Yes. You may have a medical card and hold private health insurance at the same time. If attending your GP for a referral you will need to decide whether you want to go publicly or privately. Similarly, if admitted to hospital, you will need to tell the hospital whether you want to be admitted as a public or a private patient."