A science fiction movie where a scientist couple secretly raises a female alien baby. The baby has a tail, and grows into an adult in a matter of months (or weeks). During adolescence, she starts becoming aggressive toward the woman scientist. IIRC, it was a competition thing in order to mate with the man.
Somehow, the man ends up dead, the alien changes her sex from female to male, rapes the woman and impregnates her. At the end of the film, the woman is about nine months pregnant and signing away the rights to the alien/human baby for experimentation purposes. What's the name of the movie?