Put it in the computer. Run ZAR Data Recovery Software
on it. If there's anything left on it, that'll recover it. (The program isn't free, but using it to recover photos is.)
Then format the card. If there's a problem, throw it into a paper shredder (seriously - damaged cards can be read), If it formats, put it back in the phone, boot into recovery and format it in the phone. Again - any problem, shred it.
If it formats in the phone she can keep using it, but I'd make sure there's always a backup of everything on it.
In the future, buy SanDisk cards and don't look for bargains - they're usually counterfeits. A few bucks, yes, but a 64GB Extreme for $40?