I don't know much about eggbinding symptoms but is their a bump anywhere near the belly ? We are bird owners, not vets. I reccomend taking her to the vet.
Forgive me, but I'm not a big fan of the cage or anything in it. I used to have a white one that was similar, but I quickly found that it was hard to place perches, toys and dishes within the cage.
Please, if you can, replace the cage with a square or rectangle cage (preferably wider than it is tall) with natural wood perches and rope perches.
Wooden dowel perches are not healthy for their feet, and if you are going to have a nestbox inside the cage, you need easy access to it from outside of the cage.
I'm also not entirely sure that your green budgie is a hen. Can you get us clear photos of both budgies faces with as much natural light as possible?
Something as clear, if possible, as the following images would be great!
IF you can get a front face picture would be great cause from the partial looks of it she doesn't seem to be in breeding condition. As female budgies get into breeding condition their cere turns crusty brown. I also do agree that cage is not the best as the square cages are better. BUT instead of asking more questions for answers, like I've said we can only speculate, you really DO need to bring her to a vet for a better examination if your that worried about her!