I'm very sorry for your budgie's passing.
From your description, it really is possible that your budgie has passed from a potential egg binding situation as that would explain the blood and the soiled wet feathers on the vent and surrounding areas...
Did you notice a pronounced swelling on the vent or signs of her struggling to lay? This is something that should be easily detected, especially the swelling from an incoming egg.
Again, I'm very sorry for this tragic outcome.
If you are worried about your current budgies and it's been a good while since their last vet appointment, then it may be a good idea to book them for a general health check up at the avian vet specialist.
When a hen is showing signs of being broody and wanting to nest, we have to make sure to try and discourage this by taking active measures and removing any potential nesting spots (open food bowls included and replaced by different food containers that have a top on with a small opening for feeding purposes only). https://talkbudgies.com/budgie-breedi...want-eggs.html
It's also important to keep a close eye on the hen and to see if there are signs that indicate that she is about to lay and to keep watch in case they need professional medical assistance if there happens to be an egg binding issue.