These boots are made for walking
Generally, in my experience anyway, when parents give their credit cards to their children, it’s in case of emergencies. If they get stuck somewhere and need a ride home, for example, or there’s a school resource they need immediately. It’s not for buying boots on a whim.
However, a random adult stepping in and deciding that they need to “parent” in this situation feels a little off to me. Firstly, this woman has no idea what the actual situation is, and secondly, it’s not really her place to tell someone else’s child what to do. I would have been fuming.