She didn’t always have all her memories. But look at it this way she is technically a neglected child who has become aware enough to read the room due to her previous life experience with her terrible mother. Second it’s never explicitly stated she was an adult when she died in her previous life.she could be anywhere from 14-17 realistically. She’s acts more like a preteen/teenager. She has mental maturity but not emotional maturity. I think that’s how a lot of real life kids act when they are trying to seem docile/mature.

why oh why did she fall in love w a 9 yr old they could’ve made it so that she’s still genuinely a kid that starts to remember stuff ab her previous life (or made it that she died when she was young?) or sum idk but this irks me so bad she acts like a child in some regards and an adult in others when they make it ambiguous like this it makes it more gross than anything that she ends up liking the ml which is a shame bc the story so far is p cute