Female puppy - $250 in Bronx, New York

We've just got a puppy 2 days ago, but my other dog doesn't accept her at all. She is a mix of boxer with English sheepdog, brindle colour. Her mother refused feeding the pups at the age of 4 weeks, so she is currently only 6-7 weeks old.
Rehoming fees $250.00 & references from your vet. 
Thank you!