"Don nunca le ayuda a Ana" , "Ana le mira a José" and "Sé que tú la tienes a otra" are wrong --a pronoun and the object that replaces it can't be in the same sentence. Only "Don nunca ayuda a Ana" ,"Ana mira a José" and "Sé que tú tienes a otra" are correct.
The preposition "a" is often used before a direct object when it is a proper or a collective noun.: Don nunca ayuda a Ana. Ana mira a José.