If this is a prequel as wildly expected:
Vomir. Standing over a high cliff, Cap and Red Skull are philosophizing. As the quick talks end, Cap glares into the dark abyss below, then lets go of the amber stone that he has been holding in his palm. As the glowing stone falls, it slowly fades and completely goes out of sight before reaching the bottom, where the lifeless BW body lies. She awakes, breathing heavily trying to recollect what has happened. She checks her wrist, on which the time device is still attached. Without hesitating she activates it, and disappears.
Perfect