I'm sorry your budgie is feeling under the weather.
Did you take her to an avian vet specialist? In order for your budgie to get better she will need to be physically examined and tested by an avian vet specialist, so that she is accurately diagnosed and the most adequate treatment plan is prescribed for her.
It would be best to quarantine your budgie in case the illness is contagious.
Once you have the right medication, if your other budgies start to show the same symptoms then you can medicate them as well.
For the time being and until you book an appointment, you can keep her warm by covering the cage on 3 sides.
If you have spray millet, you can soak it in electrolyte solution, this will hopefully give your budgie a little boost.
You will find detailed info on this link: https://talkbudgies.com/your-budgies-...te-recipe.html
I'm moving your thread to the Your Budgie's Health section.