That is "Marianne" and she is a maenad -- in the book, her name is Callisto.
A maenad is a nymph from Greek mythology and they are frenzied women in the thrall and worship of Dionysus who is the god of wine. Their name literally translates as "raving ones". They were known as wild, insane women who could not be reasoned with. The mysteries of Dionysus inspired the women to ecstatic frenzy; they indulged in copious amounts of violence, bloodletting, sexual activity, self-intoxication, and mutilation. They were usually pictured as crowned with vine leaves, clothed in fawnskins and carrying the thyrsus, and dancing with wild abandon. Maenads thrive on insanity, drunkeness and violence induced by intoxication and they live in the woods.
That Marianne appears to Tara who is drunk and angry is appropos -- this is a devation from the book, but I think it works. It also makes sense that she would have been attracted to the engagement party (she was on the road heading towards it), since it was a drunken fete with a murder in attendance.
We will see more of Marianne.