The author doesn't do a gob job at keeping her mental age consistent, and no, it's not because she's constantly cleverly acting like a child so the adults around her won't notice something's off about her.
They want her to know the future so she can influence it like a badass but also want her to be as easily overwhelmed as a child, so the wholesome moments will be sweet rather than akward. If you're trying to have both, at least justify it in the story: her previous memories are comming back a little at a time but her personality is still her current one or "she can notice her child brain taking over sometimes".
Seeing her inner monoIogue makes it clear she's not the master manipulator the story needs her to be.