If you plan to add UTH heat, your substrate is WAY too deep- it won't be effective at all unless you minimize substrate over the UTH. That deep is wasteful anyway. And yes, 69* IS too low.
Adjusting substrate & everything else is going to create further disruption for this poor snake. This is why we remind everyone to set up & thoroughly test enclosures before a snake ever moves in.
I'd stick to the basics- the decor makes you feel like you're doing something but it is NOT important right now- an overall sense of security for this snake IS.
Snakes drink because they need water- with or without a shed cycle. They drink more if humidity is too low. They also drink when not eating (they get some moisture from their food). Water is more essential for survival than food is- snakes (& humans+) last longer if they're at least hydrated- without water, life stops sooner than being without food, though neither is a good option.
Re- her not liking larger hides- I did mention that you'd also want a couple SMALL hides under the "false floor" for enhanced perception of security- snakes like to feel snug, wedged in- so yes, provide that always. If hides are too big, you don't need to buy new ones all the time with a growing snake- you can stuff paper into a hide to make it feel smaller while your snake grows into it.
I cannot tell you IF it will work for you to merely cover the sides of this tank- it's your snake, do what you want. I only told you what I'd personally do- & I have decades of experience with all kinds of snakes & hundreds of them at that. At this point, I'd not want to risk a further fail this snake- that's what I'm saying. Have I ever actually done what I suggested? Yup, you bet.