I might be ignorant or naive, but I just don't see how it makes a big difference whether the dog was a breeder or anything else if you want to give her a home. Teeth problems and not being spayed....I mean, she's relatively far along in life but I'm sure has several good years left, and why should she NOT spend them being spoiled and loved by you? Geeze, I can't imagine people who work at a vet's saying such a thing
. Every animal deserves a chance at a peaceful, comfortable, and loving home to spend their twilight years at, no matter what their life has been in the past.
It makes me sad to think they'd have that attitude!
I think it's kind to just enlighten you to any potential problems you might not have considered, just so you know what you're getting into, but beyond that, I think it's sad that they'd try to deter you from doing something wonderful and in preventing the (hopefully) wonderful dog from getting a really lovely home!
Good luck to you, I hope it works out for the best!