Welcome to BYC! I'm glad you posted your dilemma here. It's a great place to get answers and share your stories. I look forward to seeing your pics, too!
I'm more concerned about what you've done to fix the run so the neighbor's dog doesn't do it again. Please put my fears at ease and tell me what your setup is like to protect against predators.
Where do you plan to keep the brooder for the new chicks? Can it go into the coop, so the 6-week old baby has their company, but can't attack them? Or can you put the 6-week old baby in the same space (garage? basement? barn?) along with the brooder where she's protected and can see and hear the chicks, but can't touch them?