She's not getting enough pellets/nuggets then. Mother rabbits as soon as they give birth, should have their pellets gradually increased to unlimited(or close to) amounts over that first week. They need lots of nutrition for nursing and usually end up eating 3-4 times their usual amount of pellets to accomplish this. So 1/3 cup pellets a day for a nursing doe is absolutely not enough, and could possibly be the root cause for the babies slow growth and development as mom isn't getting enough protein, calcium, and nutrients to pass onto the babies for good growth. So I would increase the mom's pellet amounts immediately, either to unlimited pellets, or close to that amount, and also continue to free feed the orchard grass.
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If the nuggets you are using now are one of the low protein adult Excel nuggets that has lower than 16% protein, then instead of increasing those I would suggest buying the junior nuggets or another good quality 16% protein pellet with alfalfa/lucerne as the first ingredient, and using those to increase her pellet amount. She needs the higher protein and calcium content from a junior pellet. Because the sudden increase in pellets could cause possible digestive upset, it's also good to keep a close eye on her poop for any changes.
