She was branded on the face and blinded by Greshan when he was at Tentir, as revenge for Kinzi's blocking of his contract with Rawneth. In an attempt to hide the awful thing his son had done, Gerraint ordered his randon to hunt down and kill Bel-tairi.
During the hunt, Greshan was killed by the Knorth randon for hurting a Whinno-hir; Hallik Hard-hand, the Knorth war-leader, committed suicide with a White Knife rather than explain Greshan's death to Gerraint. Seeing that Bel-tairi's trail ended at a cliff edge, with only a bare rock face on the far side of the chasm, the Knorth randon concluded that she had died and abandoned the hunt. Afterwards, the senior randon called her story the Shame of Tentir.
Bel-tairi was not dead; instead, she had passed through a portal into Mother Ragga's house, where she remained until Jame showed up at Tentir, awakening ghosts.
↑ 1.01.1To Ride a Rathorn, "Chapter IV: Testing", III — " 'But what d'you think of these sightings of the White Lady? Has the Shame of Tentir come back to haunt us?' "
↑To Ride a Rathorn, "Chapter VI: The Lordan's Coat", I — " 'The senior randon call her "The Shame of Tentir," ' said Graykin."
↑To Ride a Rathorn, "Chapter VI: The Lordan's Coat", I — "The Knorth Matriarch's Whinno-hir mare, Bel-tairi, sister to Lord Ardeth's Brithany. She left Valentir, where she was visiting a new great-grand-foal among the herd, but she never reached Gothregor. There are rumors that m'lord Greshan met her in the wilderness and… well, did something to her. He and Lady Kinzi weren't on very good terms at the time."
↑Bound in Blood, "Chapter I: Naming the Dead" — " 'Impossible. Bel-tairi was Kinzi's mount, dead these forty years.' 'Not dead. Wounded and hiding in the Earth Wife's lodge. Our uncle Greshan put a branding iron to her face, all to spite Great-grandmother Kinzi.' "