Since the was between Ponyville and Appleloosa started, the mane 6 decided to make meetings because war is hard to see who we want. So they started to put Pinkie Pie apart of it. She got sad and when she got and invitation after two months of not being invited. In the way to Twilight Castle she heard Rainbow Dash and Rarity having a conversation. She discovers then why she has not been invited for meetings for these two months.