I'm very sorry your budgie is egg bound.
The best advice we can give is for you to consult with your avian vet and to give an update on her current situation. Given the fact your budgie is struggling and not coping well, you may even need to take her back to the vet's office.
In the meantime, you can keep your budgie quiet and warm by covering the cage on 3 sides with a blanket. She should be on a small hospital/travel cage also in case you need to rush her in for an appointment.
At this point, it's not advisable to let her out of the cage and to encourage her to fly. As you said, she's very weakened and the chances for her to crash land are higher too and this can be quite detrimental for her, if she happens to crash land and hit vent area that will further cause damage to her.
In order to hopefully give her a little boost, you can soak some spray millet on electrolyte solution, you will find details on this link:
This link may also be of use: https://talkbudgies.com/articles-budg...revention.html
Has the vet been able to successfully remove the egg?
I'm wishing your budgie all the best and hope she pulls through.