No, pero me recuerda a Phineas y Ferb, muchas gracias.
Está is a correct answer because this is a temporary state/emotion.
As soon as their able to make full on sentences, parents will usually start transitioning them into using honorifics so they can properly talk to older folks.
By telling how Rinko's mother goes to clean house for Mrs. ... Like the author, Rinko knows why a letter from Japan might upset a family member. Like the author, Rinko wishes she were better at reading Japanese writing.