Maid seemed to have green eyes when she said "I'll let no harm", blue eyes after that.
Omg, I didn't even notice until you said that.
Definitely something up with that maid.
The last time someone's eyes changed colors like that (Dahlia, I think), it turned out she was a demon. Maybe the maid is actually some kind of angel guardian of the family?
Anyhoo, I think there is no deeper connection between Yvonne and her mother other than the latter was physically frail and when she used too much magic, she was possessed by mares, which eventually killed her. As much as I dislike the father's interference, he is certainly justified and, unfortunately, well within his moral rights to keep Yvonne confined, especially after the stunt with the magic sword. The idea that the Villainess System is a particularly nasty mare is quite appealing, but we will have to see more confirmation before taking it too seriously.