Talk:Maud Pie/@comment-4696205-20140215081536/@comment-4905253-20140215102346

they added her a third sister because they come up a new story idea which is this one, it's kinda like the plot device for this episode.

They showed the third sister in Pinkie pride as a hint that there will be a story behind her in a future episode like this one, which will/will not explain her appearance. Well that is what i think.