Rabbits mate soon after giving birth, so this is unfortunately what must have happened.
There's few things you can do unfortunately, apart from hoping she'll sort out her babies.
Is she still caring for the older babies? Preferably they should be with their mother untill they are at least 6 weeks and not be sold before 8, but if she's acting aggresive towards them they must be removed. I have seen one rabbit raise two litters at once...but her first litter were pretty much weaned by the time the new litter arrived, and stayed with their mom and younger siblings till they were around 9-10 weeks old. (The infants were then around a week old, they had fur at least)