I have a HUGE pied budgie hen compared to her cage mate another little hen ... the sizes are so shocking. I think some breeds can be bigger in size due to cross breeding that creates the newer colors & size breeds. Your budgie looks fine & healthy, not overweight at all. If the flight feathers have just come back she will act tired after a short flight. It takes time for her to practice & get back into shape. The more she is out & about & flying with her cage mates will fix her up soon. I wouldn't worry at all.
We are not Professional Avian Vets. Nor are we Gods -(though some sb's think they are)
We can't see or touch your Pet bird. So don't trust us with its life.
GO TO A PROFESSIONAL AVIAN VET FOR MEDICAL ADVICE !