Finding the error trains your grammar ear. In 'She don't like coffee,' the verb is wrong for a third-person subject. What should it be?

English requires "doesn't" rather than "don't" whenever the subject is third-person singular (he, she, it, or a singular noun), because the verb "do" itself changes form to agree with the subject, just like most verbs take an -s ending in that same situation ("she likes," "she doesn't like").

"Don't" is correct for I, you, we, and they, but not for "she," making it a subject-verb agreement error rather than a spelling or vocabulary issue. Simply removing the verb ("not") would leave the sentence grammatically incomplete rather than fixing it.

This is one of the most common errors made by English learners whose native language doesn't mark this kind of subject-verb agreement at all, since many languages use the same verb form regardless of who's doing the action.