I had seen Twilight off to Canterlot, I had also had a hoof in there, on the mirror. I wanted to actually see it with my own two eyes. I intend to be there. I had prepared, then I set up the Hooficure, just in time for the party.
Pinkie Pie establishes a Theatre group, most for the fun of it, inviting her friends to help her out as a friendly gesture. The fun in theatre is that you can involve so many different talents in your play. Pinkie Pie loves involving friends.