They both had the same goal, but Carla was consumed by the Virus.
Make it that she never becomes the monster she was. The virus destroyed her rationality and destroyed her brain, which is why she kept screaming that "She was the real Ada Wong."
Or Ada could use the anti-virus like you're saying to neutralize it. Point is, some changes do have to be made for it to make sense, lol since Carla's lab was completely eradicated.
If you need any help, you can always ask me, since I'm Mr. Wong around here, heh.