She also rubs me the wrong way but as a kid with the reality of being in palitive care for the rest of her life
it's mind blowing to get it back(tis but a flesh wound) and with the few flashbacks they gave us she seems like she's from a well off family with a line and she had claim to power with inheritance so she only had to worry about her sickly body and the people trying to take her position in the mind of a young child (not the poverty and/or guilt that can lead to forced maturity and pessimism)
She is a probably a mid/low noble now if the current mansion is smaller that the modern one in the past life
She also hasn't done anything extremely egregious to the point of everybody thinking she is crazy enough to not be of use to the family so it's a wait and see game for everyone else
It's not like I dislike her behavior, but she's certainly not being guarded at all. She just transmigrated, or woke up her memories, and she's being... a little too excitable. There's no restraint in her words and actions(specially since she's still injured). She seems to have cunning and observation skills, yet she doesn't tread lightly. Such strange behavior isn't explained to people around her, and she's in general not being careful of her sudden change. She doesn't behave like a person who's been through hell, sickness and betrayal. I know people don't react all the same, but still, being cautious when you're in alien enviroments is just sensible.