Right answer: una
In Spanish grammar the article is a word that clearly indicates the gender and the number of the noun. Its function is to modify the noun it introduces.
In the specific case of the Indefinite Articles, we have:
Singular Masculine: un/uno
Singular Feminine: una
Plural Masculine: unos
Plural Feminine: unas
Now, in this sentence the word (noun) directora is Singular Feminine, therefore the correct indefinite article is una, and the complete sentence is:
Tú tienes una directora inteligente, bonita y alta.
You have an intelligent, beautiful and tall director.