Let's not be rude. You don't know anything about this family. Many religions forbid bare legs and arms. Or maybe her DD has sensitive skin that is best hidden from the sun.
If I were to see a little girl wearing swim leggings, her mother hiding her body from pedophiles would be far from the first thing to come to mind.
didn't this poster already answer that her dd is on epilepsy medication that makes her skin very sensitive to the sun?
One of my dd's tween friends sometimes wears a tankini top and capri bathing suit material pants - it's really too cute! and the boy shorts are adorable on girls too.