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.