EYP..isn't egg bound. It is internal laying and infection that goes along with it. Do a search on that.
My advice to you would be to have the hen euthanized, I know that is a very hard decision, and have a necropsy done. Find a state lab that will do them cheaply..you can call your local government extension office or find the information online. That way, you will know exactly what went wrong and if it is something that you will have to be concerned about with your new chicks.
I'm sorry you are going through this..our feathered friends are so hard to lose