Start by measuring the sole of the boot, toe to heel.
Take that measurement and subtract 1/4" - that's the recommended blade length for those boots.
A 1/2" gap isn't recommended at all, however some fitters recommend blades that are the full length of the sole. If you're buying a pricey blade, it allows for growth - the blades can be moved to bigger boots.
If it's any consolation, the blade was mounted correctly, flush at the front, gap at the back. The shorter blade tail would be good for synchro and dance. I don't know if it will be good for back one-foot turns, though. She might have to shift her turning point further forward on the blade, which could be difficult, especially if she changes to full-length blades.
What brand/model blade is mounted on the skate? Freestyles used to come with an Ultima Mark IV stock blade, but I don't know if that's still the case since I last bought a boot-and-blade set.