For those that didn't read the credit page:
A I U E O is the Japanese equivalent to the ABC (alphabet)
For those that read the credit page:
After あ い う え お (A I U E O) comes か き く け こ (Ka Ki Ku Ke Ko).
You'll notice that Hinata messed up a bit, notably き -> ひ (Ki -> Hi) and く -> ふ (Ku -> Fu)
Also, she used コ (Ko in Katakana) instead of こ (Ko in Hiragana).
Nowadays, Katakana is used:
[ul][*] for foreign words (e.g. コーヒー -> Kōhii = coffee)
[*] for sounds not made by humans (the barking of a dog, or the sound of an explosion)
[*] for emphasis
[*] to show that a character heard a word properly, but doesn't understand the meaning ("What's a 'biifstek' (beefsteak)?")
Note that if the word is foreign, they will use Hiragana instead ("What's a 'run day view' (rendezvous)?")
[*] when the character has a foreign accent[/ul]
This implies that while Hinata perfectly knows her ABC, she still has some difficulty with pronunciation.
That explains why she's reciting the ABC in the first place. It's not that she's re-learning Japanese, she's practicing speech.