In this sentence the pronoun <em>her</em> is B. object of preposition.
In a propositional phrase, the preposition is usually followed by a noun or pronoun, which functions as the object of the preposition. In this sentence, the preposition <em>between</em> is followed by the noun <em>Julie</em> and the pronoun <em>her</em>. Therefore, the pronoun <em>her</em> is depending on the preposition, functioning as the object of <em>between. </em>
