She got someone else's adult knowledge info dumped into her head, plus her parents were killed and she was abused at an orphanage for a while. It's like an accelerated crash course in survival and growing up. That being said, she is VERY cavalier about straight up killing people.
Less "growing up" and more trauma - what she went through is basically exactly how to turn a kid into a psychopath. I think that's hinted at by her attitude towards "adults" as a group. She's basically had to shed any capacity for empathy towards them. It's highly abbreviated (presumably the WN would take more time/go into more detail) and the glimmers of recovery from that state of mind due to the actions of Feld and Galbus seem too rapid, but especially in premodern societies where children were less sheltered from violence, I think what she's shown isn't immersion breaking.
Aside from the usual immersion breaking of a fantasy world with a status screen or equivalent skill but... well, fight the battles you can win, right?