Check if the abdomen area has a hard feeling, if yes, the problem could be egg binding due to the lack of calcium, bring to the vet to have the egg extracted, alternatively, you can try to immerse the bird's abdomen into warm water to loosen the muscles around the egg to make it easier for her to lay it.

Other signs of egg binding include fluffing of feathers, hiding at the corner of the cage base and lost of appetite.