You have gotten a lot of advice to think about! Let me add my own....
I would go and see the puppies at 6 weeks, and if you still have a good feeling about this breeder, and there is a puppy that you feel a connection to, I would get it for sure.
If the problem is the 8 wks/12 wks thing, and you feel the puppy would be better off with the mother for a little longer, I would try and work something out.
If something seems off, or she won't keep the puppy until it's a good size and eating well, walk away.
I know your heart is broken over the loss of Millie. I hope you find a little one to help to heal it.
