My girl has medium escapades and wears a size 8 in Nike vapens. The vapens are a size bigger shell then all other four pairs of boots. They fit in the medium with room to grow. The ankle and toe strap have another hole for more adjustment.
I can try to take a picture and show you if it helps. Nikes are the biggest boots I've come across far as outer shell.
So we tried a medium escapade with her stupidly fat Vans boots...I'd never recommend a pair of those...to anyone...ever... The boots are so snug in even a large binding that if there were any snow in the binding, they would certainly not fit. That said, we reluctantly went for a burton lexa in size L and bought some upper end DC boots. I suppose that's what we get for going cheap last season! Live n learn...
Lexa's are sick bindings. They are the girl version of the Malavitas and I've never heard one person complain. The hammock heel cup really holds the boot down well without cranking down on the ankle strap.