Look online for term papers and how to write them, then assign her one. Have her choose a thesis to write a persuasive essay on. My kids are doing this in college all the time.
The thing is, I know how to do all of those, but I just need some sort of thing to do on a regular basis (I'm not in twelfth grade by the way, but I just need at least that level). And I couldn't take a college writing class until next year, since this semester's already started, and next semester I'm going to be in London. Plus, I'm only fourteen so, I don't really want to.
On Writing Well by Zinsser (sp?) and The Elements Of Style by Strunk and White are great books. Also getting a MLA guide will help with the citation and foot noting aspects of research writing. Some colleges and Universities have their course outlines online. Perhaps your student could follow such a course of assignments.