Labradors are great dogs all around. I do not know if you've raised a puppy from 8 weeks, but retrieving puppies explore the world with their mouth. If the pup doesn't nip at the moment, expect it when you get her home when teething kicks in. I would definitely consider rescuing a dog or finding a foster home that has dogs up for adoption -- this way you won't have to deal with a mouthy puppy.
I'm not even going to touch the part where you mentioned putting the dog down but please contact a rescue or foster group before you consider putting another dog to sleep.