My 3 yr old recently had to get a cavity filled got a shot to numb it now i'm noticing the inside of her cheek has white stuff could she have bite it?

Definitely: Children & adults often bite their cheeks, tongue or lip after being numb for a filling. There is a new, but expensive medication called OraVerse that makes the numbness go away much more quickly. It is being used a lot with children and adults with disabilities & those that need to speak right after dental work. It is not a good choice after having an extraction or some other procedures.