Have you candled them again to see what they look like inside?
Sounds like the hen has determined they are duds.. and I essentially would have to take her word or in this case her actions in the matter for it.
There can be many reasons for them not to hatch.. I don't think that 7 was too many...
Very likely.. that's too staggered and she needs to leave the nest for those that hatched earlier. Sounds like she is doing well!
Congrats on your lovely little family! 🥰