You must first find her at school to begin interacting. After raising her relationship level slightly through talking, use the "Ask" command to get her phone number.
But if you have typed that phrase into a search engine, you are likely not looking for a simple character download. You are here because you have questions. Who is she? Why does she look so perpetually uncomfortable? How do you make her act "in character"? And most importantly—how do you solve the technical hiccups that come with installing her?
You will need high Charm (at least 200) to progress her storyline, which can be gained through specific jobs like "Drug Dealing" or training. Relationship Progression Steps