You're right; in French, there is no elision with possessive adjectives: The final -a from ma, ta, and sa may never be dropped. But be careful — the abbreviations m', t', and s' are not possessive adjectives; rather, they are reflexive pronouns. Example: Je m'ennuie (I'm bored.)
To avoid awkward pronunciation with possessive adjectives, use mon, ton, or son before a feminine singular noun that begins with a vowel or vowel sound:
Right: Qui est ton artiste favorite? (Who is your favorite artist?)
Wrong: Qui est ta artiste favorite?