Si, es una maestra en la escuela.
What does this translate to in English? And should I use ''hey'' instead of es'
Hey is an English word, and is "oye" in Spanish. Professions always take the verb ser.
Or do you mean "hay"? That would mean "Yes, there is a teacher at the school."
The correct Spanish should be "Sí, es maestra en la escuela." The article isn't needed when stating a person's profession, unless the profession is modified with an adjective or the like. The translation is "Yes, she is a teacher at the school."
I don't understand what you mean by "And should I use ''instead'' of es'"