The one thing that isn't conveyed as well in the show as it is in the book is that Sansa has had a lady boner for Loras ever since the knight's tournament in Ned Stark's honor when he was named Hand of the King. They allude to it some on the show, but in the books she already was in love with Loras from afar.
So in the book it is literally a dream come true scenario for her. To marry the man of her dreams and get to leave King's Landing for Highgarden.
Of course without her inner most thoughts, it is impossible to convey that on camera. Plus, the show runners probably figured that it wasn't that essential because she has been so tormented in King's Landing that she would probably marry an untrained gorilla if it meant getting the hell out of King's Landing.
But for the non book readers this is not just a means to an end to get out of King's Landing, this is a dream come true for her.
Well that's interesting because from my point of view she has been THE most gullible and naive character in the series.