Looking for the word that displays the point of change, the apex, that point or event that changed something it was the "" of the day, her thoughts, the game, etc.
I believe the phrase you are looking for is turning point. M-W
a time when an important change happens
The Collins dictionary shows a few alternatives that I like, such as "crossroads":
crossroads, critical moment, decisive moment, change, crisis, crux, moment of truth, point of no return, moment of decision, climacteric, tipping point
A google search for
turning point synonym shows "landmark" amongst other options - which I quite like, depending on context.
I also like "watershed", see M-W.