Isn't あたい some kind of childish dialect for "I" ?

Aknos said:
Isn't あたい some kind of childish dialect for "I" ?

Yes, that's how Cirno usually refers to herself.(mostly in doujins)

She could not write down the last letters, yet have the strength to write 3 epilepsies.

Oh god, Cirno. Your timing is either unlucky or impeccable.

Aya?
Akyuu?
Aki?

Even Atai could also refer to Komachi or Orin.