Thanks for the chapter!
Seems like she's afraid of storms and falling water. Hard to tell with just an image here and there but seems like she drowned to death in her previous life, likely during a severe storm. Not sure if that trauma is just combing with trauma of being locked in a box by her mother into being afraid of drowning while trapped in the box. That or if mother, through abuse or neglect, caused a few situations where MC was locked in a box and it was filling with water due to mother either throwing her into the water to murder her before changing her mind or box was just left somewhere without thought and turned dangerous due to a storm. Like being left on a roof, rain got into the box through the top or air holes (need something to let air in so didn't suffocate,) but bottom of box too sturdy to drain the water quickly so started filling up. Or out of way place that flooded, box too heavy to float so started filling up instead.
In any case good to see family values her, but vague warnings on not to meet mages without explaining why always ends up with person learning the reason the hard way. Just guessing, but mages are likely able to go around due to being useful and powerful as long as don't break any laws, or at least get caught doing so similar to nobles. As for why she'd be in danger likely because being Castiello she'd be a very tempting prize as either a rare spell reagent, valuable sacrifice to the demon mage affiliated with, or a brood mare to have children with potential for even higher magic power than the average mage. Would be really funny if makes friends with a demon who then decides to protect her despite being such a prize.