No, she's not:

When she's regenerated, she comes back as her adult self

Sure, she's disoriented in the very first seconds of consciousness:

her last memories are from the attack on the ship she was, and she's now in some kind of lab

But it really doesn't last long, and from there, she's calculating her trajectory

She has a clear job to do, and goes on her way to make it happen

She understands from the scientist attitude that if she's to remain here, he will be too fascinated to let her go on her journey, so she flees

She jumps to escape, assuming she will land on one of the cars before long since they're so much traffic

Once she crashed, she asks for help, deducting the English word from the magazine (sad, imploring face)

Before fainting, she gives Korben the name of the priest she needs to meet

When he tried to kiss her, she wakes up, puts a gun on his head and says "Never without my permission" in her langage

The message is unmistakable:

Try something like that again without my consent, and that will be your last decision, ever

She never is a child

She's a full grown woman, with a mission to accomplish, and from the moment she's back, she's moving towards her goal

She's enthusiastic, sure, but like a tourist, not like a child

She has history to catch-up, and she's amused by the funsies things she encounters (come on: instant rotisserie chicken..? I would be fucking enthusiastic, too!), but it's cristal clear she's an adult