In Resident Evil Revelations 2, the main antagonist is known as "The Overseer". When examined closely, it becomes apparent that the Overseer shares many characteristics that Carla heirs before her mutation at the hands of Project Ada. This leads me to the conclusion that Carla is the Overseer. I will explain my reasoning in the following paragraphs.
Appearance: The supposed photo of the Overseer raises much speculation about who this taunting fem may be; note the following features of the Overseer: she has light, long, and blonde hair, she is a caucasian female, and she is noted for wearing white clothing.
Let's put this into perspective, Carla, before her mutation, had long blonde hair, she is caucasian, (and of course female), and she also seen wearing white lab coats often. Coincidence? I don't think so.
Assuming this is all a coincidence, there is still evidence to support the theory of Carla playing the role of the Overseer. Let's carry onward.
Before Resident Evil: The Marhawa Desire and Resident Evil 6, (Carla's first appearances), she was experimenting continually with the samples she collected in 2001. Carla's work on the virus began with a sample of the T-Veronica that she had obtained, intending to use it as the basis for her new virus. Managing to isolate the mutation characteristic found in the Progenitor and subsequent viruses, she succeeded in creating T-02 by combining this characteristic with the T-Veronica virus. She needed test subjects, of course, therefore, causing her to command her infantry to capture civilians. Finally, in 2011, she has optimized her B.O.W.s to perfection, and needs to test their effectiveness against trained agents, hence, Claire Redfield. She most likely knew that by her capturing Moira, Barry would come to the rescue, allowing her test it on both of them. Subsequently, she captured Moira to get to an actual experienced agent into play - Barry.
Now, there is one crushing detail that partially disproves this theory: the events in Resident Evil Revelations 2 take place in 2011, Carla was transformed in 2009. Meaning that the Overseer could not be Carla at this time. Although, she may have pre-recorded the voice clips that play over the P.A. system, further enabling the theory that she is not even at the island at the time that Claire and Moira are. Furthermore, in the opening cinematic, their is a part in which we are watching Moira and Claire hugging on a monitor screen - this may be the Overseer's isolated area for her to watch over her test subjects. Think about it, if is able to set up cameras in the Terra Save building, imagine where else she could have camera access to. We also know that she has cameras set up on the island as well. This is certainly a controversial topic.
With the appearance of the Overseer strongly representing Carla, and her whereabouts are accounted for, allow me to move onward to some more interesting evidence.
On the wikia for Resident Evil, if you look at one of the photos in the Overseer's gallery, it is titled "The Woman In White". This is where the Resident Evil history comes into play. In Resident Evil, the first one, Jessica Trevor refers to the Umbrella scientists as "The men in white", arguably because of their lab coats, in which are white. Now, Carla is an Umbrella scientist (Neo-Umbrella), who is noted to wear a white lab coat in her times of experimentation. I believe the connection between the two names is quite obvious here; they are referring to Overseer as the scientist who injects the test subjects, as in the first game. Drawing to the conclusion, that if the Overseer is Carla, it is Carla who brought upon this new virus. Hence, accounting for her unknown years of experimentation. It all makes perfect sense.
So yeah, this is my friend and I's theory on the Overseer's true identity, let us know what you think!