OK, this is from the Theatrical Version commentary on the Directors Cut DVD. Sometimes Ridley Scott is talking with Sigourney Weaver and other times on his own
"We didn't know how she (lambert) died. The implication was that there was kind of a sexuality to this adrogenous male female (alien) who could give birth itself but could also impregnate......there are insects like that so we based that on good old mother nature and um was that some dreadful ending, some terrible invasion of her (lambert's) body, a rape, and therefore would there be a version of the Cartwright (lambert) character? There would certainly, whatever happens, be more humanoid aliens now on the craft and thats what she (ripley) now has to destroy"