House Webber
Lords of Coldmoat, whose banners bear a spotted spider on a silver web. Lady Rohanne — the Red Widow, four times wed and four times widowed — holds the castle in her own right, with a long red braid, a longer memory, and a deadline in her father's will.
The fuller tale
Coldmoat flies a spotted spider on a web of silver thread, and its holder in this generation has earned the sigil's reputation for patience twice over: Lady Rohanne Webber has buried four husbands, and the neighborhood has never quite stopped whispering that competence like hers in a woman needed a darker explanation than simple ability.
The truth of her situation is less lurid and considerably crueler — her father's will strips Coldmoat from her unless she remarries within a year of her fourth husband's death, which means the castle's most capable ruler in a generation spends that year defending her own inheritance from the very document meant to secure it, poison rumors circling the whole time like an unwelcome dowry.
The dispute with her neighbor at Standfast is entirely of a piece with that competence: when Ser Eustace Osgrey's household diverts a shared stream to his own fields, Rohanne answers with a dam of her own, a burned wood, and a willingness to escalate that few marcher lords twice her size would have matched — the Red Widow does not lose ground she considers rightfully hers without a fight.
Coldmoat runs on more than Rohanne's own will. Her castellan, Ser Lucas Inchfield — called the Longinch — and Septon Sefton keep the holding's daily business turning, a household competently staffed enough that even its enemies rarely accuse it of being poorly run, whatever else they accuse its lady of.
The feud's resolution answers both problems the same house had been quietly wrestling with — Rohanne's deadline and Eustace's pride settled in one wedding, an old rivalry converted into a shared roof. History would eventually have more to say about her red hair and her nerve than the marches ever guessed: by a later match, Lady Rohanne Webber becomes an ancestress of the Lannisters of the main tale's age, Coldmoat's blood running, generations on, all the way to Casterly Rock.
The page and the screen
Lucy Boynton was cast as Lady Rohanne Webber for the announced second season, based on The Sworn Sword, which was not yet airing as of this writing; Coldmoat, the water dispute, and Rohanne's marriage to Ser Eustace remain, for now, unfilmed.