This is almost certainly egg binding. Take her to the vet as an emergency. They will probably give the bird a hormone treatment to make her expel the egg, and maybe antibiotics. Give plenty of cuttlefish (for calcium), which should be crushed up with the back of a spoon. A good quality mixed cage grit also provides essential minerals and calcium.

My female Parson's finch needs 2 teaspoons of crushed cuttlefish every day.

Without Vitamin D, calcium cannot be absorbed. The best source in my opinion is egg food enriched with Vitamin D supplement.

Vitamin D can be produced from sunlight but window glass affects the quality of light and there is no benefit.

Birds affected by egg binding may be able to produce hard-shelled eggs if their diet is right, but a vet told me that some birds which have a good diet are prone to this anyway because of genetic reasons, or because the bird is very young.