|The title of this article is conjecture based on information revealed in the A Song of Ice and Fire novels or related material and may be subject to change.
In the books
In the A Song of Ice and Fire novels, Barbrey Ryswell is the head of House Dustin and the widow of Lord Willam Dustin, who fought alongside Ned Stark during Robert's Rebellion until he was killed in the Showdown at the Tower of Joy. Lord Roose Bolton was married to her late eldest sister, Bethany. It isn't clear if Willam left an heir, because Lady Barbrey continues to rule House Dustin in his name. She usually leads House Dustin to act in concert with House Ryswell, which is still ruled by her own father Rodrik Ryswell.
Lady Dustin has wrinkles around her mouth and eyes, but she is still tall, unbent and handsome. Her hair is equal parts brown and grey, wearing it tied behind her head in a widow's knot. She usually dresses all in black, but she sometimes accentuates her attire with vair. While she is intelligent, she has grown into a bitter woman over the years, among other things due to her husband's death.
In her youth, Lady Dustin was infatuated with Brandon Stark, who took her maidenhead. She claims Brandon loved her and never wanted to marry Catelyn Tully and that the match was made when Lord Rickard Stark's maester, Walys, put the idea in Rickard's head. Lady Dustin is extremely distrustful of maesters in general and refers to them as grey rats.
Lady Dustin was quite fond of her nephew Domeric, and as such loathes his bastard half-brother Ramsay Snow openly, whom she suspects had a hand in the former's death. She keeps referring to Ramsay as "the Bastard", presumably because she knows how much it angers him. Ramsay dislikes Lady Dustin and has malicious intentions toward her, but his father forbids him to harm her, as after the Red Wedding, she is one of the few truly loyal vassals House Bolton has.
During Robert's Rebellion, Lord Willam was among those who were summoned by Eddard Stark. Lady Dustin begged her husband to send any of his kin in his stead, but he was too proud to let anyone else lead the Barrowton levies. Eddard returned Lord Willam's horse to Lady Dustin, and told her that Willam had died an honorable death, that his body had been laid to rest beneath the red mountains of Dorne.
Ever since, Lady Dustin holds a grudge against Eddard Stark, even after his demise, for not bringing her husband's bones north with him so she could bury him at his ancestral home. She intends to pay him back by feeding his bones (which, in contrast to the show, have not been brought yet to Winterfell) to her dogs. Her hatred towards House Stark is not limited to Eddard, as she states "All my favorite Starks are dead".
When Robb Stark summons his bannermen, Lady Dustin has no wish to reinforce the Starks, but sends as few men as she dares - knowing that she must give Robb some or risk the wrath of Winterfell. She also uses that to her advantage: her men keep her informed about the location of Ned's bones.
Lady Dustin is one of the guests at Ramsay's wedding. She, not Ramsay, tells Theon he should give the bride away because he is the closest thing she has for a brother. It is unclear whether Lady Dustin is aware of "Arya Stark"'s true identity, but if she suspects the ruse, she is wise enough to keep her doubts to herself.
Lady Dustin has a keen sense of observation: during the wedding, she notices that Roose does not touch any of the meals or the drinks, unless Lord Manderly tastes them first; she also notices that Lord Manderly behaves too joyfully, maybe suspiciously, for someone who must feast with his son's murderers - and serves the meat pies himself to the Boltons and Freys (she has no idea about the true contents of the pies, though). She knows well that Lord Manderly would have turned against the Boltons and Freys had he been brave enough, and that many of the other guests who lost their kin at the Red Wedding - the Umbers, Hornwoods, Flints, Cerwyns, Tallharts, Slates - would have done the same, since "the north remembers".
Some time after the wedding, Lady Dustin and Reek go down to the crypts. There she reveals to him why she hates the Starks, and warns him not to repeat what she said. They notice that several swords are missing from the statues, but they cannot guess the reason.
Lady Dustin disapproves of Ramsay's cruelty toward his wife, claiming that "Lady Arya’s sobs do us more harm than all of Lord Stannis’s swords and spears. If the Bastard means to remain Lord of Winterfell, he had best teach his wife to laugh". She is also, like many of the northern Houses, contemptuous of Roose's allies in House Frey, as a large number of the soldiers she sent with Robb Stark died at the Red Wedding.