Poopy problems might also have something to do with the MVB. Get a reptisun and give her one to two weeks, if she's not back to normal then there may be another, underlying issue. In the mean time give her baths every day and rub her tummy, a lot of people don't like "excessive"
bathing but it's been my experience it's easier to get a poop daily when you do this. All of mine get daily baths as "potty time" and they rarely go in their tanks, won't simply WON'T poop in her house, haha. It's at the point now that they know what the bathroom means and Kira has actually taken to pooping on the counter while her tub fills up :lol: .
Also, if she keeps hiding
after the UVB has changed it might be because something in her viv is not to her liking. Mika used to hide in the most awkward places until we gave her a hide with a sand box, which seemed like a godsend to her for a while, then she got sick of it and started
black bearding whenever she went in it, so now she has her binky folded up under her hide and she snuggles down in that when she doesn't feel like basking. She does bask properly, on her own now and is just altogether happier.
That said your first concern if the uvb change doesn't help is to rule out any actual health issues, then if she's in the clear, see if your beardie is environmentally temperamental like mine, haha.