Concept

Scheming Matriarch

Tropes

Grew up in the ducal household of the Southmark, married off young and pushed to do her duty of bearing many children, but found herself having to "help out" more than expected and practically ended up running the house. They never had any children, and some have speculated that she pushed him (not literally) to his death.
Eventual marriage to Thurston II went better, but she had already learned how to get her way. (Ended up as his Spymaster.)
Still has strong ties to the Southmark and House Thornbull
Though not a Highhorse by birth, she has taken it upon herself to guide the house to greatness, for her children's' and grandchildren's' sakes, at least
Still entitled to the income from the Dowager's Portion of the Arl's estates, until her death
Convinced Arl Thurston III is a bumbling fool that must be "cleaned up after," and is barely able to prevent herself from saying so out loud

Husband #2: Thurston Highhorse II (926/975 @49)

Son: Arl Thurston III of Banner Hall; (51yo)
Son: Baron(-Consort?) Ser Sterlan Highhorse of [in Iron Hills, Southmark]; (48yo)
Son: Elderman Symon Highhorse of [City Ward]; (45yo)
Son: Vicar Almus Highhorse of Chapelton; (39yo)

Primary: She's trying to develop her plans for the family—currently working to get Ser Chadd married to Princess Damsel—but is being hampered by budgetary issues brought on by (what she sees as) the Arl's frivolity and spendthrift (including, but not limited to, his recent ransom for the release of Garak Highhorse
Secondary: Trying to get rid of or replace the current Steward, and looking for dirt on him, but hasn't been able to find sufficient justification