So where does the myth of "Virgo the Virgin" come from?
Many goddesses who are linked to Virgo mythology are assumed or considered to be virgins, though it is unclear whether the confusion over the meaning of the word "Virgo" is the reason why.
One statue of the goddess Artemis of Greek mythology is portrayed in a statue as having fifty breasts, which is representative of her nurturing life on Earth. Interestingly, Artemis is considered to be a virgin. The Spring goddesses, Persephone (Greek mythology) and Proserpina (Roman mythology) were assumed to be virgins as well, though they are more correctly tied to the Virgo myth via their mothers Demeter (Greek mythology) and Ceres (Roman mythology), the goddesses of the harvest.
There is also a myth about a young girl named Parthenos in Greek mythology, who died young and was placed in the heavens (presumably as a constellation). The Virgo constellation would be the only fitting place for Parthenos, whose name happens to literally mean "virgin".
So now we have three sets of goddesses said to represent Virgo - the Harvest Mothers, the Ladies of Justice, and the Youthful Virgins.
Logically, virgins cannot be mothers, though when you get to Christian mythology, we have the virgin Mary giving birth to the messiah, which further confuses things. The fact is, mythology is far from being science, and as such, these things can happen quite easily. All you have to say is "it's the will of the gods" or "it's a miracle", and that is all the explanation that is necessary.
One could argue that all three of our Virgo groups could be considered "self-sustaining". The virgin Spring goddesses help create life, while Ishtar is often linked to Virgo mythology and is the Babylonian goddess of procreation. Similarly, our Ladies of Justice were known to be nurturing as well. Astraea, the Roman goddess of justice, was the last of the celestial beings to leave Earth, and only after she was tired of taking care of a humanity that insisted on destroying itself.
Astraea is perhaps the most interesting character involved in the Virgo myth, as she is a virgin, represents justice, and was a caretaker of humanity. After leaving Earth, she is said to have been "placed in the heavens", which is most likely why some mythologists believe her to be the constellation "Virgo" itself. Many mythologists suggest that she became the constellation Virgo and her scales of justice became the constellation Libra. This is a good argument, though one could argue that she, in combination with her scales, could have become Libra, not Virgo, though she represents them both in certain ways.
All things said, Astraea is easily the strongest contender for the character represented in the Virgo myth and is who I strongly correlate the stories with.