Technically...carla IS a costume...she is just the 3rd version of ada (excluding retro)
All you Carla haters can do get bopped. Carla is QUEEN.
How? are you clearly reading? or just speakin "fanboy" carla is a CLONE of ada. therefore she IS an alt version of ada. the only thing different in game wise is obviously her loadouts and unique speech, same ada voice same ada melee.
"I'm sorry squeeky, it's just a game, you got to get before you get got"
^ Yep. Carla and Ada are two entirely different people, but they look exactly the same and Capcom probably didn't want to put in the effort to give Carla an alt when she is both a "throw-away" villain and the doppelgänger of Ada. Besides, herself before being Adafied seems to just be Allyson from Resident Evil 5, whose long hair would be hell to animate, and her lab coat seems to be a bit of a stretch to make into an alt.