Is there any special reason why "a girl" is neuter?
I don't know, probably for whatever reason it is in German.
Or in Irish its masculine XD
Really? Chairman Wow, that's a bit freaky!
Mind you, after some Irish girl's i've seen, the reason can be pretty sound
I'm guessin it's because they are announcing the fact, but I am not sure. If I was going to make that statement to someone though, I would have said "Αυτή είναι μια κορίτσι." Could be wrong though.
"Αυτή είναι μια κορίτσι" is not grammatical correct. The word for girl (το κορίτσι), as well as the word for boy (το αγόρι), is neuter and that does not change according to the context.
The word for "child" is also neuter (το παιδί).
It's good. It gets you used to the fact that grammatical gender is arbitrary, early on.
But boy «αγόρι» is also neuter. However, if that annoys you, there is another word for the girl, somehow poetic, that is feminine «η κόρη».