It isn't love at first sight.
Love at first sight doesn't exist. Not for her.
But it's love.
Their first meeting isn't memorable at all. She sees him, but she doesn't really see him. To her, he is nothing more than another nameless face.
She takes a seat on the other side of the room, and that's the end of it. When class ends, he stands up and leaves and she doesn't have a reason to follow.