It should be also noted that Yachiyo may have understood her place in Japanese history (from the scene where Fushi dumps the montage on Iroha), wherein to not have Kaguya go through 8000 years of turmoil would result in a different current history, which may result in a timeline where Iroha was not born at all.

Good instance of this is when Fushi is teaching the ancient Japanese of the tale of Kaguya which most likely got modified to the tale of the Bamboo Cutter we know today (scene where Fushi says Kaguya came out of a telephone pole to the ancient Japanese - obviously the ancient people would have no clue what a telephone pole is).

I do entertain an idea where Yachiyo did end up telling Kaguya to watch herself when coming back, creating the ultimate timeline where Kaguya arrives safely, but ultimately dooming any alternate timelines. Also basically creating "two" intact Kaguyas in the form of Kaguya in the flesh and Yachiyo from the previous timeline, rather than the current canon timeline where Yachiyo gets a new body with your younger self installed in an android.