How can simulate her drowning in a black water, something like oil. We will have green screen of this scene later, but for now I just wanted to know is it possible to do this simulation? and how? Actually I need a clue for this purpose. I want have this natural as much as possible. For example the wave's movements should be very natural according to her hands and body movements.
For something like this you can either go the 3D way with Blender like it was suggested or another 3D package and build a 3D body double, match the moves of the actor and have that interact with the 3D liquid, or go a different way and use FreeForm Pro by itself or with the AquaPack and create a combination of animated displacement maps and masks that can create the same effect. Either way it will be a lot of work. Good luck!