"Our mother is a doctor."
Translation:Nuestra madre es médica.
Because you exclude indefinite articles when talking about a person's profession.
When to use and when not to use definite and indefinite articles in Spanish is a minefield, this might help explain some of the exceptions:
I used "es una doctora" and that was accepted. Is there a difference between indefinite article use for médica and doctora?
I feel like I've seen examples before where it would be "A nuestra madre" - Why is this just "Nuestra madre"?
Our mother is the subject of the sentence, and won't need an a.
You may be thinking of a case where our mother is the direct object and would need a "personal a": Amamos a nuestra madre. We love our mother.
Or probably a sentence where our mother is the indirect object: A nuestra madre le gusta leer. Our mother likes to read. (Reading is pleasing to our mother.)