I guess it all really depends on what you would like her to write about.
I find that things I struggle with such as tasks, limits, self esteem issues and my basic understandings of a D/s relationship are those that I am asked to write about.
I procrastinate so I have to write about that, why I do it and why I shouldn't.
I was also asked to write about the things I enjoy. My cello playing for example, I write about how I feel when I play, what I do, and what I study, etc.....


If she is interested in something specific, that she has little knowledge of, have her research it and write a few short paragraphs about it.

If she is struggling with her thoughts and stressing out from writing them down, maybe try and ease up on the assigment. Don't give her a wordcount, if she wishes to write a paragraph or three, let her use her own discretion.
Tell her that she doesn't have to write out a well formulated essay, maybe have her do it in point form. Tell her to write down thoughts as they come up. I know I stress out quite a bit because I cannot write or formulate my thoughts as well as everyone else can. I in fact hate posting because of that.
When she becomes more comfortable with writing out her thoughts, you will notice it will become easier to her in time. To me writing is a practiced thing, the more you do it, the easier it becomes.
Even have her take an online writing course, there are some free ones out there, and it does help.

For more ideas try this link, it is related to all things D/s but there are a few good writing assignments there.

http://www.sensual-service.com/categ...urnal-prompts/