did you forget the abuse and trauma she had from her past life???
IIRC we didn't get any flashback with the butler... and she faced the black haired duke who at face value seems quite a lot scarier than that pathetic butler? Even that arsonist dude they met seems scarier than that butler? When she's already overcome the experience of accompanying the duke to the country's worst prison to see a death row inmate... letting her plan go down the drain just because of some scrawny lone butler who *trespassed* on the scary duke's territory, completely on his own, is anticlimatic, when one as a reader still hasn't been told about there being anything specially scary about that butler.
he was the right hand man-therefore most likely he was involved directly with the harassment from the staff, abuse from the family, and poisoning. People who have been abused tend to have tendencies toward accepting abuse as normal. She did not want the ML abused and took control of the situation the best she could. For example, when the ML father runs her into the ground with training she doesn't complain even when she collapses. That is not what a regular well adjusted person from a loving family usually does.
Girl, you say you got the ind of a 20 year old and you know he's just a tresspasser, so why are you so afraid and agreeing to go with him, so darn easily????? Why you acting like that scrawny butler of your previous in-laws was some undefeatable threat, like a secretly trained assassin (he certainly doesn't look like it????)