[cooperadymas]

It's clear that they don't know how to handle her powers and are doing the best they can, albeit yes, it was probably the worst way to handle it. They were scared that someone would get hurt by her powers (check) and that, if discovered, she would be deemed a monster (check).

Furthermore, the troll king's advice was that Anna could not know about her powers or the damage from being struck in the head would return. So their only choice was to isolate the two sisters from one another.

There was nothing intentionally villainous with the parents.