YANBU, they are too high for someone of her age. As you've already pointed out, the potential for damage to her tendons, muscles and joints is too high if she wears them regularly.
If it's only a couple of hours a weekend, then I can't see that being much of an issue, so long as she's not going on a 2 hour hike in them (can't imagine why anyone would!) - but the more she walks in them, the more risk of damage there is.
Since it's her father and there's already antagonism, I'd let her keep them at your house, refuse to let her wear them and then conveniently forget to let them go with her to her father's.
But what the hell was going through his head when he agreed to buy them for her? Especially at that price! Does he often do the "disney dad" thing? Urgh!