Theory: Birdo's Princess Peach Disguise

Abstract
In Mario & Luigi: Superstar Saga, Birdo’s Princess Peach disguise is created using a Peach’s Crown power-up just like the Super Mario 64 DS Cap power-ups.

Arguments

 * Argument 1: The crown Birdo is wearing is an exact copy of Princess Peach’s Crown, similar to how the Magical Hats are exact copies of Mario, Luigi and Wario’s caps.


 * Argument 2: Birdo becomes an exact copy of Peach physically, the same as what happens to whoever picks up one of the hats in Super Mario 64 DS.


 * Argument 3: While physically identical, the voice remains the same. We know Birdo’s voice remains the same in her Peach disguise as it angers the Beanstar when Cackletta attempts to use it. This is also true for whoever uses the Magical Hats in 64 DS. Whenever a character transforms into Mario, Luigi or Wario, their voice remains the same.