Comment on Dear IDW 2 by Shieltar
Personally, I'm amazed SEGA didn't take the opportunity to release there entire roster of characters, including the freedom fighters as DLC replacements for Origional the character in sonic forces. It would definitely have boosted sales significantly.
TBH, it's been said that Sally was designed after Ricky, one of the animal buddies that is used in the classic games as a battery source to power the Badniks, so that may be why she is not used in the games.