I think the plastic bag noise could be a natural instinct, like a snake or
maybe something moving in the leaves, so a natural flight kicks in.
sounds like you are doing things right.
3 weeks is still a very short time with some gliders, only thing I would
maybe change up, get dried or live mealworms, you say "she will relax and
she has come up a sniffed the treats." I might, once she is relaxed, slowly
open cage door, move my hand halfway to her slowly, then see if she will come
get the treat. just sit and wait for a few minutes see if she will come to you.
if she just runs and hides, go back to trying to get her to take a treat thru
the cage bars. I also put treats in a container and give it a small shake, this
sound brings 6 gliders to me.