Which means Either Ada Is no longer A villian Or She is Tricking leon into thinkin She isn't the cause of the Outbreak In Resident evil 6. That She Really is Working with the BSAA Now Or She is Secretly Still A Organization member.
I think all evidence so far suggests that you're right. In the recent videos for Ada's scenario (the beginning of this one: [link]) Ada looks down on a ruined town and is surprised at what's happened to it. She also says 'that poor town'. That doesn't sound like the sort of thing a villain who releases viruses would say.