Wow! That’s a crazy start to you new journey with a new rabbit! Im glad the breeder was able to take the babies. I do know they can foster to another mother relatively easily. I don’t know what type of affect that has on the rabbit that originally birthed them, to be honest.

I would call the breeder about the new nesting behaviour you are seeing. It might be something she is familiar with.

There is the risk of them retaining a kit and those don’t usually survive. It can also put the Does health at risk, so a visit to the vet might be in order.
Sometimes a rabbit from the same litter can be born a few days later but Im not certain about a whole week later. Maybe the breeder has seen that before?

Another possibility is if there was a fertilised egg that implanted later then the others and has only now come to full term. Or an egg was released later and still fertilised. I do not know how often something like that could occur. Or perhaps it is just hormonal and a bit like a false pregnancy.
Years ago, I had read it was possible for rabbits to have dual pregnancies due to their having 2 uterine horns. So if she was with an intact male again, a week after the 1st incidence, it could be possible she got pregnant with a 2nd litter then…

That breeder is a moron, I think you should take her in for your own piece of mind.

I’m sorry you’ve had to deal with all this.

Hopefully, this is just a “false pregnancy”. It could be, because rabbits don’t have heat cycles like dogs or humans, they can ovulate and become pregant the minute they’ve given birth (and as Jersey also points out, there have been cases of rabbits carrying two litters of different developmental stages at the same time, although it seems pretty rare). If/when a rabbit ovulates, she will have a false pregnancy if there’s no male around to impregnate her. Her body will “think” she’s pregnant and the maternal hormones released will make the fur, especially on her chest, come loose so it’s easy to pull off and make a nest of.

This is a little sad, so don’t read if you’re sensitive: Sometimes, as Jersey says, not all kits get born. A kit can get stuck in the birth canal. This invariably means the kit dies (and all other kits that may be in there). There are cases when a stuck kit mummifies inside the birthing canal and sits there permanently, without harming the mama bun, but it seems more common that a retained kit will be delivered eventually. A vet can palpate (feel) the tummy or do an ultrasound to see if there is a stuck kit, so if you are worried a vet visit is of coutse the safest thing. 

How is her appetite and poop?

ETA: I just saw a rabbit special on TV, where a vet explained that intact does can ovulate if they are being pet by their human. The doe can respond to pets like it would to a male. So maybe if you have pet her since she came to you and she wasn’t used to getting pet,in her old home, that could have induced ovulation and an ensuing false pregnancy. The vet in the rabbit special also said a false pregnancy tends to only last about 2 weeks, whereas a real pregnancy lasts 31 days. False pregnancies always resolve spontaneously.