Withered Tweetie appears to hardly resemble the original Tweetie model from the original Jolly, except she is now withered (mostly on her arms and legs) and lacks segmented face plates. She is now noticeably missing her beak as well as the feathers on top of her head. She has a big rip next to her left eye, and her torso is covered in what appears to be dents, along with yellow glowing eyes. There is what could be rot on her body as her color is now brown instead of blue.
Tweetie has the exact same model as Fantasy Tweetie, with the main difference being the head shape, the lack of a beak, the obvious signs of withering, and the hands being the same as Withered Jolly's. This doesn't mean that they are the same robots though.
To further imply this, Tweetie's hands were different in the early demo of Jolly 3: Chapter 1, as they resemble hands from the Fantasy animatronics of the first game.
Withered Tweetie was later confirmed in 2022 to be a prototype model of Fantasy Tweetie.
In the game's demo, Tweetie actually had a different pose when in the Main Security Office than she has in the current game.
Tweetie's transcript includes a typo for one of her lines, one being "Let me lift you up and make you fly!"