I also recommend to get secondhand check your local sites where people sell&buy secondhand, playpen or baby fireguards would be great and you can get really cheap sometimes in excellent condition like new. Of course you disinfect before you start using them.here is a photo of the setup for now. the gray box is the nest box while the blue box is the litter pan.
yes, she has been living with her older babies until now. I have put them in a different enclosure for now.
The nest is in the cage but she keeps messing with it and uncovering the little ones.
I will purchase another playpen for her. What do you recommend for a decent price?
I think this cage is too small and she has no room at all, no wonder she gets stressed. If this cage is high enough you can add a piece of wood to make a shelf for her it would give her some extra room, but in my experience those cages are rarely higher than 50 cm, but still you can add a little shelf.
If you don't have any other place to keep her you can remove the nest and put it into a large cardboard box (think like banana box or bigger) and place next to her cage that would make some kind of extension she will see her nest and you will let her out for nursing. But that will only work for the next couple weeks as after that kits will start exploring territory and will be able to get out from this temporary cardboard box anyway, you will need to build much larger gate so they can be all together. Where are her older kits at the moment, you said you removed them from the cage they are still 4 week old?