She may have acetoanaemia/milk fever (like preg tox just post-kidding) and may also need calcium. LOADS of branches - ivy is good for getting their appetite back, but as much as you can find of willow, rosebay willowherb, thistles, hazel, beech etc. Nettles (she may not want them fresh, some of mine will have them two days dried, others won't touch them even then), chickweed (minus the roots, just cut off above ground), and if grass is all she eats - we cut ours long grass (incl thistles) with the scythe/strimmer with scythe attachment and they love that on a rainy day.
any kind of brassicas - if you don't drink the milk at the moment any "cabbage taste" shouldn't matter
oat cakes or other kind of simple biscuits like digestives
jst thinking about things I have tried...