I would introduce her to the Millie Fleur in side by side cages, inside if necessary. It is not fair to leave her in the pen for the roosters to gang up on. She is at a definite disadvantage. Most chickens need a buddy, and the two of them may get along just fine. I am assuming the Millie...
This is so cool and the chick looks very healthy.
I am thinking about the poo thing too. Maybe when it gets older a vet could amputate the extra leg ? It looks like it would get in the way and stay pretty messy most of the time.