She looks very healthy and her enclosure looks pretty good, though I don't know what bulbs you're using or what her 3 temperature zones are, but she looks good..
It looks as though you have either a Reptisun or Arcadia tube UVB mounted inside her tank, which is great...Is it a 10.0 tube UVB (it's not a 5.0 UVB is it)? And is the tube UVB older than 6 months? I've seen this happen before because the owner forgot to replace their UVB tube and it was not putting out any UVB suddenly. It's an easy thing to forget about doing, so if her tube is older than 6 months that is at least part of the issue...
I'd be willing to bet the problem is that you gave her superworms! I've seen this many times before with healthy beardies that are of a healthy weight, and since they can afford to not eat for a while, once you introduce them to superworms, which to them are almost like treats, they are like "What the hell is this" when you try to give them crickets, BSFL, or roaches again. So I'd be willing to bet that she's holding out for only superworms, as you said she's still eating the superworms.
She's not dying, not even close. If it is by chance a medical issue it is most likely parasites or Worms, which will upset their stomachs enough that they lose their appetites, but when offered something that they really like, like superworms, they'll still eat them. You said your vet did not do a fecal test? Was this vet a certified reptile vet, or just a general vet or exotics vet? A fecal test (gram stain and microscopy) is typically the very first thing a certified reptile vet will do when a beardie becomes sick, because parasites and worms are very common in them, and the fecal tests are pretty cheap. If you can either call that same vet and ask them if they will run fecal tests if you drop off a fresh poop sample to them, or if they refuse then find a reptile vet who will no doubt run a fecal first, I would highly suggest it. She may just need an antiparasitic and possibly an antibiotic or antifungal along with it depending on what the tests show. They typically clear up pretty quickly after they start the meds, but always, always, always, no matter what the vet tells you, always put them on probiotics along with the medications too, because the meds can really upset their gastrointestinal systems even more and kill off the healthy bacteria in their guts. The probiotics given in conjunction with the medications will keep her feeling good and get her eating again, in fact you might want to put her on probiotics right now once a day, because if it is parasites or Worms causing her stomach to be upset, the probiotics can make her feel better right away, and they don't hurt them at all so it's a good idea.
Again, I'd get the fecal testing done regardless, just so you can definitively rule parasites in or out, but I'd also be willing to bet that if you completely stop the superworms and let her not eat for a few days, she will eventually go back to eating her regular feeders. But I understand how difficult it is to not feed them anything at all. The only reason I suggest this is because of how many times I've seen this happen after superworms were introduced...And check your UVB tube!