The full context is here
https://en.touhouwiki.net/wiki/Perfect_Memento_in_Strict_Sense/Kaguya_Houraisan
Not sure im fully understanding the last bit but, its her manipulating small moments in time which are composed of instants (unchanging moments) and acting on them.
Which lets her "have multiple parallel histories" at once.
Think its worth mentioning history in touhou tends to just refer to the events and reality of specific things sometimes from peoples perspectives and this does bring up the perspective of humans as well.
If this is the case then isnt this just more referring to multiple different perceptions of herself due to manipulating countless unchanging moments faster than anybody can percieve?
Her just flat out creating multiple universal timelines on ability that describes nothing like that and at most doing it by hax is a serious stretch even for a possibly rating to me.
Possession or being in charge of something doesnt normally mean much anyway unless its having some kind of physical reality bending power over something.