The "purest of all blood" is fresh out of the bone marrow, i.e. in your circulatory system.
Menstrual blood is a combination of blood, some mucous, and dead endometrial tissue.
The endometrium consists of a single layer of columnar epithelium resting on the stroma, a layer of connective tissue that varies in thickness according to hormonal influences. Simple tubular uterine glands reach from the endometrial surface through to the base of the stroma, which also carries a rich blood supply of spiral arteries... Proliferation is induced by estrogen (follicular phase of menstrual cycle), and later changes in this layer are engendered by progesterone from the corpus luteum (luteal phase). It is adapted to provide an optimum environment for the implantation and growth of the embryo. In the absence of progesterone, the arteries supplying blood to the functional layer constrict, so that cells in that layer become ischaemic and die, leading to menstruation.
So, menstrual "blood" is a combination of sloughed off stromal and glandular tissue, broken down vascular cells and blood, and, no, it is not highly oxygenated (it's kind of darker than normal blood. It doesn't carry any "decoded DNA". It's basically a waste product at this point, dead, dying and no longer functional tissue.
Virgin's flow is just as dead as non-virgin's flow. Cultures obtained at hysterectomy indicate that the endometrial cavity is normally sterile. The major difference between a virgin and a non-virgin is that the possibility of infection of endometrial tissue exists in non-virgins.
Of course myths will arise around menstrual flow. After all, when it was alive, it was the medium for implantation of a blastocyst. But they are just myths.
Infections as a Cause of Infertility