I've been seeing a good deal of discussion about Kris not telling Susie why Noelle left or what happened with her dad, and it's understandable why people frown on them for it. However, if you pay attention to how things play out, you'll realize it wasn't exactly done out of ill intent.
Aside from the fact that it would be SUPER OUT OF CHARACTER for them to not care about Rudy's health (seeing how they were literally praying for his welfare last Chapter), they weren't actually trying to stop her from seeing the Holidays! In fact, they were not only leading the way, but they were DOING SO WITHOUT OUR INPUT!
So why did they stop? Because Susie tried to investigate Asgore's shop. And so, because that would most likely lead to her discovering the code and compromising the plan/promise they'd been trying to fulfill before they even met her, Kris had to make the difficult decision to make the Dark World in hopes it would prevent her from ruining said plan/promise!
Remember, people! Kris doesn't do the wrong thing unless they feel it's for a really good reason, which has been a feature of literally every single important character in UTDR (i.e. Toriel using fire magic against Frisk to prevent them from leaving the ruins, Chara pressuring Asriel to aid their infamous buttercup, etc)!
But didn't Kris make the fountain after they already saw that Susie stepped back out of Flower King with some flowers? And based on the end of the chapter, Kris knows the shelter code is in Flowerys soil, there's no way Susie would have looked there. Not to mention Susie had no reason to look for a shelter code in Flower King at all, as she only learned that Asgore was the former police chief later from Flowery. Kris making the fountain is what led Susie back inside Flower King, and gave Flowery the opportunity to tell Susie about the codes location.
Like I could maybe see Kris initially panicking when they saw Susie enter Flower King, which is when they removed their soul, but after Susie left Flower King again, making a fountain in the shop is literally the least helpful thing Kris could do if their goal is for Susie to not find the shelter code.
One could also argue that Kris probably prepared the Flower King fountain in advance the night before chapter 5, as Kris turned over the TV and made a deal with Seth before making the fountain, which they maybe wouldn't have done if they were under time pressure (though I wouldn't say that's super strong evidence, Kris could have turned the TV over quite quickly, and their deal with Seth seemed very vague, just "help us out at any point during our adventure and I'll reward you", so it's still possible they could have done those things right before making the fountain).
Like, I agree with the other points you're making, that Kris has been shown to be concerned over Rudy's health and likely has something they consider to be a very good reason to work with the Knight, but the idea that Kris made the fountain to stop Susie from finding the police code just seems pretty illogical to me, unless I'm missing something BIG.















