
Not really, the 16 years she lived in this life were as a kid growing up, you can't add it after 18 because she didn't live that as adult, she even forgot her memories. Not to mention both her families were extremely neglectful towards her, it will have some effect on her. As a person with a neglectful family (not as bad as hers) I totally get it.
This is not just about meeting an "annoying kid", every moment of her childhood is related to this. She is not his mother or nanny to punish and push him to improve, she has her own problems too.
I agree with the greenhouse part, but didn't she has a use for it? (I don't remember exactly).
Yes her brother is like that because of upbringing but lets be real, a person can't always be understanding, there is a limit, she has been forgiving her family for 16 years but there is a limit, you can't always force yourself to forgive others even if they are not directly responsible.

I totally agree with you.
I see this not having some beefs with a kid. I'm actually impressed how she interact with the kid. If it's the other, they already killed him. but her, she let him study magic he was restricted too (because of their mother), loosen some burdens and let him do what he wants as long as it doesn't get in her way. She still sees him as a family despite the hardships she got because of him.
But for me, I'm totally okay for them to make up but once they are older like in their 30s or something. Since they have to focus on growing and learning for themselves.
Technically she's lived 18 years of her first live and 16 of the second, so 34 years experiencing this world and she beefs with a bratty 12 year old? To the point of destroying the greenhouse that holds the memories of his dead mom? and she doesn't even need it for anything important.
If the kid is spoiled then be strict and teach him better, or push him to improve. If you really hate him then ignore his existence, but have some self awareness as the more grown up of the two.
And I'm pretty sure that in that scene she was about to physically hurt him. That's normal between actual siblings that are close in age, but not if you are a reincarnated fully grown woman with a lot of strength. I've met annoying kids who tried to bite or slap or whatever, but I've never had the impulse to hit them back.