I have an alto player that sounds like she's majorly biting her instrument! It's her second year on the alto and every time I tune her it changes right after!
What are some techniques you have? Or maybe ways you've explained it that your students understand?
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)