She may or may not want her egg. There is really nothing you can do to force her. How old is she? Is the pair actually bonded or do they just share a cage?
Do not buy an incubator unless you have the skills and time to feed a brand new tiny 3-4 gram baby every single hour for several days, and then every two hours, every three. And so on. And feeding a day 1 chick is nothing like feeding a larger chick, they can aspirate on half a drop.
She needs a lot more greens and other veggies as well as egg food which you can either buy or google recipes for. She should be OFF SEEDS if possible before her eggs hatch because some parents don't break the seeds down far enough for young babies and it can cause major digestive disasters.
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Cockatiels:Battle, Sniper, Jackie, Honi
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