If you consider how she grew up and isolated, can you really blame her for finally getting to be an actual child and live like one, but also helping where she can? The Empress screwed her over time and time again, this time, this Empress can't do shit to her. She can act how she pleases without worry now she knows her father and brother actually adores her unlike her first life where she misunderstood.
Also, if you go back to the first chapter, she wasn't even an adult when she died. Her mental maturity was only between 15-17 (or if this story does 20 years old as a sign of being an adult, it would probably be up to 19 she could have died), even then as I stated, she wasn't able to live like a child and died as a young teenage girl.
Did you read the first chapter?
She acts like a child because her body and mind didn’t finish synthesizing. If I remember currently it’s around 10-12% maybe a little more right now (it’s goes up a little every birthday) but that why she acts like a child, her body probably won’t handle her adult mind.
It's so hard for me to read this knowing mc is reborn only to act like a child. Even on latest chapter she goes and confronts thugs ( I didn't finish the chapter, had no intention to) like miss gurl you're a child (physically, and I doubt she's becoming mentally as well) and has no way to defend yourself let alone another person