With any second-hand skates, look for:
. no rust on the blade, an even (front-to-tail) chrome reveal stripe, intact bottom toe pick and a decent curve at the front rocker.
. eyelets that aren't stretched or worn, all hooks intact/not bent, sole flush against the bottom of the boot.
. lack of deep creases at the ankle and the front of the boot.
Some ankle creasing is fine - it means the skate was properly broken in and it's probably now the right stiffness for a beginner.
If the boot has no creases whatsoever and wasn't used for very long, it might be too stiff. The Royall was a very stiff boot.
Leaving the top hook undone helps temporarily with knee bend, but it doesn't address the issue if the boot is too stiff to allow ankle bend. Unless she can bend her ankles/knees and extend the bent knee over the toe, it's probably too stiff. It's probably an older skate that's been stored, so the leather may have dried out and will therefore be even more stiff until it soaks up some sweat, lol.