But the mom does have a valid reason to
She already stated the actual reason she's wary of him is not just because of nobles but rather because he doesn't have a clear motive and was hiding something which seems to be have been proven true judging from chp 26 (it it's prob not bad intention but on their pov it does seem sus)
The mother’s actions are totally valid. First off you have to look at it from their perspective and not someone from the 21st century… Like in those type of times nobles did whatever they wanted, and killed peasants like them if they acted “out of line”. Also given her past if it had gotten out she would have been labeled some kind of harlot, even now if it was made known not only hers but her daughter’s life would most likely be ruined.
So it makes sense to be so guarded and negative towards this guy they’ve only known max a couple of weeks. That and given the recent behavior of the soldiers/nobles during the war it makes sense to be suspicious of Bert. We know he’s not tricking them but, from their perspective he easily could be.
It’s not like they live in a society with rights. Also now that she’s confirmed his noble status to a certain degree there’s the complications of social class between them. Even if Bert is sincere society won’t look kindly on them. She wants her daughter’s happiness, but not at the cost of her daughters safety and future stability
Oh yeah, Franz and Anna are definitely siblings and I hate her mom so much. I get she had a bad experience with a playboy noble but that doesn't give her the right to treat Bertram like that since he clearly isn't flirting with or trying to take advantage of anyone