I FUCKING KNEW IT!!! is what i would be shouting out if this wasn't the most obvious "plot twist" ever that was fully predictable from page 1 of chapter one.
It was one of those instances that, if it would eventually have a plot this was the obvious route, but I am surprised that it decided to have a plot instead of just keeping it a gag manga.
She either loved him from the start or fell in love with him later on, she probably just wants to stop him from going on his mission to keep him safe now.