Hi Tinah,
<em>I </em>is the first person singular English subject pronoun. When another part is added to that subject, it doesn’t change case and become an object pronoun. If you say <em>I want to walk to school, </em>you also say <em>My sister and I want to walk to school. </em>
<em>Me </em>is the object pronoun, so it receives the action of the verb. It also does not change when another part is added: <em>My mom drives (my sister and) me to school. </em>