You could have diet issues - Take away grain, offer both hay and straw to eat, and offer free choice baking soda to help settle an upset tummy. If you want to get more active about it, give her a dose of liquid Pepto.
You could have parasite issues that bloomed under the new conditions - Check for anemia and for coccidia. If you are doing your own fecals, that's great. Otherwise you can take a sample to the USDA extension office. Coccidia doesn't cause any other symptoms until/ unless it's acute, so the goat's perky attitude could be a mask. Coccidia can really stunt their growth if not kept in check, so it's definitely a concern when they are young.
ETA: The professional fecal test came back with heavy tapeworm count, mild worms, light coccidia. I recommended Valbezan, as it is labeled for tapeworms. The goats were dosed and are now back to regular poop.