try giving it greens occasionally even though most dragons that ive heard of dont like them you can trick them on occasion by handfeeding it or if you can get it to open its mouth a tiny bit stick the food in and that sometimes triggers a feeding response. that doesnt work all the time though.
maybe a tiny dose of Ivermectin if it somehow got worms or some paracite of somesort (not recomended without first taking a fecal to be tested and talking to a veterinarian)
if this is the first time shes done this in three years she may just be burminating. sounds very similar to what my frilled did about 6 months ago. it just sat sulking in its cage and wouldnt eat hardly anything for about a month and a half. how big is the enclosure? if its to small then it could be a comfort thing.