@gorion You're talking about her not asking the yandere to come on her trip right? Honestly I think that's realistic, people are often bad with communication and don't want to trouble people. That's something I have first hand experience with, I should ask someone a question, but I feel like I'd be bothering them even though it's probably no trouble at all.
Also in this case I think it's also for the best, some distance between them is probably good. I have a feeling if the yandere was around her all the time the yandere would probably go even crazier. Right now she's able to have some self restraint with those yandere urges. That's my interruption at least.
Edit: Part of what I mean is right now their relationship is working. No one is getting chopped into pieces and/or locked in the basement. Things are fine. No need to upset that balance, even more so when yanderes have a very careful balance of sanity usually, very little holds them back from going completely off the rails.