"Is she a teacher?"
Translation:¿Ella es maestra?
It's explicitly incorrect, according to the RAE. See definition 1.1 here:
I've heard that "estar" conjugations are for something temporary and "ser" are used when something is more or less permanent. I am temporarily happy but i am always an American. Yo esta feliz. Yo soy un americano. Of course the line if temporary vs permanent can be fuzzy. In any event, I tend to think that this idea is really cool and a shortcoming of English. Perhaps it's the incentive behind "e-prime". (And that's a facinating read if you've the time.)
In Spanish, a question is denoted by punctuation ( ¿Ella es maestra? ) if written, and by the upward lilt of the voice at the end of the sentence when spoken. The word order doesn't change. I don't know whether that is a hard and fast rule, but that is the way Duo teaches it.