You're supposed to be shocked or confused just like the protagonist... After all, the ojousama didn't even wait a week to confess, it was the next freaking day lo/ so the author is going for that "what the hell?!" Factor.
Whatever is going through her mind, it's a mystery right now.
I probably would have been a bit taken by surprise if I didn't know it was already gonna happen, it's literally shown straight away that she asks her out and then it backtracks
I feel kinda meh about the sudden confession, like MC has found someone to be a real true friend to her and yet instantly has to deal with her crushing on her, i think like end of the next chapter after they hung out or something would've been better instead of like BANG straight off