Stress can also cause them not to poop regularly... at night, they need perfect darkness to sleep. If you've got light on at night (even if it's a night bulb that's black) they can still see light, and it will keep them up. Or half awake... they just won't get good sleep, which could be stressing yours out, resulting in the odd BMs. Unless your night temps drop below I think it's 60? (someone please correct me if I'm wrong here) you don't need extra heat at night. I know they don't live in stark barren desert in the wild, but they do live in some pretty dry and sparse areas, and if you've ever been in the desert, you'd be amazed... it gets COLD at night!
Personally, I'd try taking out all lights at night, and taking out the heating pad too, or putting it all the way under the tank so the glass and the carpet is between the beardie and the pad. It's not much of an answer, but it's something to try that might help.
If she's not warming up enough after eating, she might not be digesting her food well. I had to play around with basking spots for Taz before I found one he liked, that got up hot enough for digestion. It ended up being a stacked pile of slate I picked up at the local yard decor place.... it seemed at first that if the basking temps got too hot, he wouldn't bask, but I just had to find a good basking spot, hehe. That might also be something to try.
I would try these things first before oils in the
bath...
Off the top of my head, I'm also thinking about foods that would be diuretics... but I can't think of which ones they are. Those ones will make her pee more, and loose more water in her body, which would constipate her, etc... you can see where that line of thoguht is going.
Last idea I've got, boils down to parasites.
All these are just ideas (from mainly a novice at beardies!) but you might find something to go on that works here. Hope it all gets settled!