I'm sorry about this chick's beak. But thankful she's the only one so far and that you have a good plan for your breeding moving forward. Just know it's not anything you did to cause it, these things just happen sometimes.
In that case, I think it's a random congenital defect that Easter eggers are prone to, like cross beak. I have been curious if this chick and the others were related to stock from a particular hatchery. Sounds like it's just random. And very rare. Only four posts about this that I can find.
Do...
Hi! Oh goodness, I just saw two threads about chicks like this. They were Easter eggers.
I need to find them. I'll link them in my next reply.
The issue was that the upper beak continues growing while the lower beak does not. The lump is the back of the chick's tongue.