I wonder if its gonna end up that she can only make accurate predictions when she is in love?
So when she moves on from the boy to find a career in prophecy, she finds out it stops working then and there.
For that EXTRA special gut punch to her, since torturing this girl seems to be the core goal of the story.
My personal 'this is rather fucked up, but I wouldn't put it past this author' expectation is this:
There's some kinda power in the glass orb that is trying to help Shirahoshi
It may have subconsciously influenced her to use otaku to help Shirahoshi earlier.
And when she actively want to help, it just give her instruction sheet to guilt trip Tamura back to friendship.
Maybe it'll make her an offer directly later: Be around Shirahoshi to keep her power and have to watch Shirahoshi and Otaku pair (assuming author doesn't pull surprise yuri ship later) or leave and lose her power.