How are you tuning her and to what note?

If it's changing right after, she's not playing the same when she tunes and when she plays her music. You may need her to play her current concert music and tune her that way.

I am a sax player. I have no idea what you mean by "it sounds like she's biting". Is she too tight in the embouchure? Have her go to her low range. If she struggles on low notes, then she needs to work on opening up her embouchure (unless instrument is out of adjustment)