it's probs since she's a grown adult in a little body where she already knows what to say, is just waiting for her little brain/body to catch up.
Around that age would be the earliest she can become more human and less baby (forming proper phrases, walking, etc) and even as an adult she was more special than the average person is what makes it "believable" for me. Maybe giving her a lisp might make it better I guess but I personally don't think it's too far off since my niece can actually talk proper now too (she's 3.6yrs old) tho more phrases than long sentences and it's seriously impressive. I know she's def not the norm but still not impossible

I know this is like fantasy and all that, but couldn't they make her a bit older than 3 years old idk man like a 6 years old would've made a bit more sense.
Also hilarious that the age part is the only thing I can't parse lol.