Howdy Raisingpeeps
I do wish I had a simple answer for you but unfortunately I do not as there are so many variables.
As it is your first hatch, I am guessing that it is also hers? Not knowing what kind of a mumma she is is just one of the variables. Some mummas will take any new babies they can get their wings on while others not so much.
Do you know why the first chick died? Could she have squashed it?
I actually have no personal experience with introducing chicks to a broody hen, but I have had a few hatches with broodies.
Me, personally, with a first time mumma, as she has one chick to raise, I would leave her with that chick, see how she goes. If I had a broody mumma whose hatched chicks all died, I would definitely try introducing some 1-2 day olds.
Mumma hens and chicks bond early on in the piece and I personally believe this bond is created days before they hatch while they are still in the eggs. My broodies definitely increase their ‘talking’ to the eggs prior to hatching.
Not only are the 7 days old chicks possibly at risk of her attacking them, as the bond has not been formed, they may be afraid of her.
But, if she is one of those wonderful mummas who will accept anyone and anything, it may work out.
As I said, too many variables and this basically comes down to whether you want to give it a go or not. You may have a happy ending but you will also have to be prepared and have a Plan B.
Hopefully someone else may chime in with some good advice and personal experience with a success story.
Please let us know what you decide and how you go.