here is how -

have her play a sound on only the head joint, be sure she stops up the open end against the palm of her hand.
check her embouchure, the mouth should look normal with the corners a little firm, the lower lip must not be tight.
as she blows a tone, have her move the jaw back until a low sound is produced...pushing the chin forward helps produce the high pitches.

she could be overblowing...tell her to blow gently.
some kids start low, some start high...you teach whichever they can not do and then they can do both...sorta

keep us informed!

dj