It's in event 11 on map 324: Desert.
Hmm, I understand. A lot of people have also said even though they understand her motives, it's still hard to forgive her. I'll try to take this into account with future content for her
Viewing post in Rinny's motivations during her second route comments
Maybe it comes down to it being slightly underestimated quite how much Rinny likes the MC? I haven't had the chance to check out the yandere content yet (I'm definitely going to!), and I could be wrong but I personally came to the conclusion that Rinny legitimately loves the MC, and that's why it was also a bit easier for her to come to her decisions. Thus, I was able to forgive her more easily with this in mind, especially with her honestly believing the MC would be happier that way.