Has she ever been wormed? Have you done a visual FAMACHA score... eyelids, gums pale instead of pink? Do you have a relationship with a vet that you can take in some "pellets" for them to do a fecal for egg counts for parasites?.
Not seeing them it is hard to make any suggestions... but worms is the number one killer of many "thin" animals and if not treated quickly, they literally suck them bloodless from within.
My suggestion would be an oral wormer, use half strength if she is that thin and weak, to knock some of the possible worms out, and then re worm again in a week... goats and sheep are a little different... but one thing, if you hit them "heavy" with a wormer, the worms can die in the gut tract and they will actually poison their system before being expelled so sometimes you have to do it in smaller doses.
My best advice is a fecal and a vet trip. If she is full of worms, they could IV her with some nutrients while administering a wormer and hopefully give her some energy to get past it.
If the fecal comes back and it is not worms, then there needs to be a better exam by the vet to try to determine the problem.