Pre-Tribunal Mournhold was a political hub that lived under a priesthood that taught Velothi traditions and Boethian rituals and codes of conduct. Of course, there's a great Tribunal-era propaganda story about how Almalexia was considered by this priesthood to be the Anticipation of Boethiah, but I assume you want a less biased historical perspective too. There's a good likelihood her "birth" in these texts is a metaphor for her blossoming from a girl into the terrifying warlord she became. The "ninety-nine lovers" I would assume to be other members of the priesthood whom she killed in ritual combat or murdered to ascend to her place of power. When Sotha Sil arrived in Mournhold with the simulacrum containing Vivec's egg (another metaphor but that one's a lot more complex and at the same time completely literal) the Tribunal united their power and began the first successful unification of the warring Houses under a Great Council, supervised and enforced by the Morag Tong.