Hi! First of all, I think the absolute MOST important thing to say is that I'm so so sorry for your loss, and I hope that you're gentle with yourself. Regardless of whether you can look back on this as a lesson learned in the future, I hope you give yourself plenty of room to grieve before you worry too much about learning from this.
Secondly, the only thing I know of related to hormones which could cause sudden death like this is egg binding, but I will say that I find it to be rather unlikely that that's what happened. Yes, some birds are just prone to egg binding, and it can be more common if your birds are missing certain vitamins/minerals in their diet, like calcium. But typically egg binding happens because a hen is a chronic egg layer, laying egg after egg after egg, and depleting her body of energy and resources.
IF (a big if) egg binding was the culprit, there are certain signs that, if you notice them, can help you identify egg binding quickly enough to save the bird. Egg binding can kill a bird in less than 24 hours--but leading up to death, you tend to notice them straining to lay their egg, tail bobbing, lethargy, general sick behavior. If you catch it quickly enough, a veterinarian can surgically remove the egg. Any attempts at home to help "push" the egg out could break the egg inside of them, which can be quickly fatal. Again, though, I'm telling you this so that you can think back on your budgie's behavior the day she passed, as well as keep an eye out for it in the future, but I don't think this is what happened to her.
If you're ever unsure what took your bird's life, often the only way to know the cause is to take them to a vet for a necropsy. Having not done that, you have no way of knowing for sure what took your bird--and there's not much we as strangers on the internet can do to clear that up for you, except for perhaps throwing some skepticism on the egg binding theory.
