Eve

Eve was portrayed by Natasha Henstridge. She was the clone of the original Sil and mother of Sara and she appeared in Species II and had a brief appearance in Species III.

About
After the death of Sil a clone was created from her. She was called Eve. Through medication and complete isolation from the outside world and from having males in her environment, Eve was made more human than alien through education and subjected to numerous experiments by a team led by Dr. Laura Baker for the US military to find ways of defending humanity from the threat of the alien species they indirectly had encountered.

She is recruited to stop another half human and half alien creature called Patrick, when they become aware, that she can feel her presence and that Partrick is attracted to her and vice versia. She finds him and copulates with him while Baker, Lennox and their allies deal with his offspring nearby.

Then she helps defeating Patrick, but is gravely wounded by him. Later she is killed by another creature called Portus while being transferred later by an ambulance, but not before giving birth to Sara, the result of the copulation with Patrick.

Trivia

 * Unlike Sil, Eve was raised less like a test subject and more like a human with bubble kid disease. Thus allowing her humanity to develop and be nurtured. So once hee alien mating instincts was sated, her human side reemerged.