I would need a castle for all of the memories I have. I take it that you do as well?

[the Red Wedding holds a tricky place in Margaery's mind. it's true that it did stop the war for the most part. it's true that House Tyrell benefited from it. it's also true that it was a horror and she had to try and comfort Sansa Stark, Robb's sister, in the aftermath of it]

It was a dishonorable way to defeat Robb Stark, but the Lannisters never cared about honor.