Nice one! That's what Peach looks like in Mario Party 2 & 3, so it's the right era.
I can't remember the exact instructions, but I entered a code into Paper Mario and I was able to have Peach as my main character instead of Mario. Would have been a bit weird when my Peach met the kidnapped Peach though!
Peach was one of the characters considered to be in the first Smash Bros., but never made it due to time constraints and the Nintendo 64's technical limitations. Same with Bowser, Pit, King Dedede, Mewtwo, and Meowth.
Yeah, Meowth was almost a playable character in the game.