You definitely need to keep the adults in separate cages after the baby is fledged. That nest box also must go after the baby has fledged. Tiel hens are notorious for turning any nook or cranny into a nest, and that nest box is always going to be way too tempting for her.I saw that they have chick also, until that baby has fledged you can't do anything. it takes both parents to raise the chick to fledgling. please be ready to buy a second cage so that you can separate them once that baby/ies fledge.
Also, unless an egg is physically broken, I'd leave it until the chick is fledged and the hen is out of the nest box for good. 'Tiels count eggs (yes, they count), and they will replace any missing egg with at least one additional egg.
It's also why "flooding" with eggs isn't necessarily a great idea. If a hen thinks that she should have, say, 10 eggs, because she is being flooded with eggs, then 10 eggs she will lay in the future. This is one of the issues we had with Buddy.