My dutch rabbits react very badly to to much greens, especially when they are very young, when i have a litter i do not give fresh greens to the doe and kits until they are about two weeks old, i feed the mother on Spillers High Protine pellets. if the mother feels threatened she will sometimes eat her offspring in order to "protect" her young, remember that they normally give birth underground in small spaces, so being in a barn is not normal, try providing her with a small hutch to nest in.
Like someone else has said domestic bread rabbits have been bread in ways so that he normal rabbit diet is not as good form them, they do not receive as much nutrition, wild rabbits are a lot smaller than most domestic Bunny's.