Okie doke, so I went and got a better infrared thermometer and some small furniture sliders to get better clearance for the bottom of the tub, and so I could attach the UTH underside of the tub. Used handy foil tape and got the UTH onto the tub so now we wait to see if there's improvement in her temps. I also noticed a minor curve to the bottom of her tub when I flipped it. Not sure if it's heat warping or a detail I didn't notice on the RUBS (really useful bin).
There was about a 2 degree different between the New Thermometer (Klein Tools) and the old Ryobi thermometer, so I'm going with the Klein reading. Tub was reading 84-88 on the tub base before I made any changes.
Took out Coco, since I figured flipping over her tub with her in it was a horrible idea. She didn't hiss or strike, though she wrapped around my arm / watch, most likely to get warm. She did a little exploring and some tongue flicking, though still sure she wasn't a happy hatchling.
I placed her hides and water back in, then put her back. She went back behind her cold hide again, so she was not happy...at least I know what scared Coco looks like.
Tonight I'll power down my computer so the lights aren't blasting into her tub and take the towel off.
Fingers crossed that I'm making proper adjustments! Thanks for your help everyone!