All "Request for Independent Study" forms require that a proposal be attached. Obviously, a well-written proposal not only helps keep the student focused, it also helps avoid subsequent misunderstandings about the quality or quantity of work you expect. If this thesis is a two-semester project and part of the first semester work involves narrowing the topic, you and your student may not be able to attach a fully developed thesis proposal to that semester's independent study form. In fact, preparing a full proposal may be one expected outcome of the first-semester's work. But even if the first-semester proposal is broader and more tentative, you still want to be as concrete as possible in terms of what you expect the student to accomplish and how you intend to evaluate the progress. You and your student can look at sample proposals by using the link in the student section of this website.
Note: If the research involves human subjects, your student will need to seek approval from the university's Institutional Review Board. You will need to help your student understand this process and file the appropriate paperwork.