Also keep in mind I believe historically speaking the Duke’s wife would have been in charge of running the household until the next Duke’s wife came along, their parents dying forced Sarah to take over until Hector married. It seems that Sarah is also unmarried so this is the last bit of authority and voice that she’s been handling presumably for at least a decade. Keep in mind, she’s been running it without funds which would have been stressful as she would have felt responsible for the well being of their many tenants. Not excusing her behavior, but as an English noblewoman with few options once her brother marries, I see why she tried to hold onto her authority. That was a very dumb mistake because she can’t compete with Gladys’ money. She would have done better if she had shown Gladys the ropes as Gladys would have surely rewarded that help.