so to add fuel to fire, the question has been answered a dozen times It could mean either, he, she or it IS not a girl since the subject is missing BUT those that have pointed out that unA and ragazzA refer to female are correct If the sentence was non e un ragazzo, then it would mean that he, she or it is NOT a boy!
The perfect translation to this sentence from Italian to English would be "This person, whom is not gender specific, is not a girl." Meaning this person could be a boy, woman, or man, or... 'other'? Anyway, whomever it is, it's not a girl. That's the only reason that it's unA and ragazzA <-- note the capital letters. If this sentence as part of a lesson was Non e un ragazzo, it would be "This person, whom is not gender specific, is not a boy." The same could be done with donna, uomo, etc...
"non" is Italian for the English "not" "Non é una ragazza." is not specific. "It is not a girl." would be good for that as it is also not specific, but "She is not a girl.", "He is not a girl." and "You are not a girl." (Formal singular version of you) could also be translated to that Italian sentence. One would hope the context would be clear to help out with which.
Oh! And, sorry it took so long to reply. :P Okay, so Not means Not means, well, not. e means is. Una is the way of describing a female with the word a. It is a bit confusing, but you just have to go with flow. ragazza is girl, and so the sentence appears to be, "Not is a girl.' But you actually move the word not from the beginning of the word to the correct place, so it would be, 'is not a girl' now, I know that the 'she' is not in this sentence, but it is not required to understand what they are trying to say, because, 'is not a girl', it is kind of obvious that the she is not needed to make this sentence clear. There may be a more proper rules for not having the she in the sentence, but as far as I can assist you, that is all I know.
Can I ask something ? In some series( or films) , We can see it, we can hear some dialogues (plural version of word) like "It's not a girl, or ıt wasn't girl"... I hope you understand. I think the response(correct sentence) would be [ It is not a girl. ] Non é = it is not. Am I right ?