Much of this is going to be entirely dependent on what you have to prove and what you are going to use as evidence. Without knowing the exact dimensions of the assignment and what needs to be proven, it will be difficult to determine what would be a good thesis statement. If you are looking for items upon which to write, I would think that you could delve greatly into how Gruwell uses literature to connect to the lives of her students. In being able to identify the issues of identity and acknowledgement of voice through historical content, she is able to link content and student experience together. Another topic to explore could be how Gruwell uses the writing process as a way to build community. In a process of composition that is fairly individualistic and devoid of much in way of forging connections, it might be really interesting to see how Gruwell makes writing a communitarian element, merging the subjective with the collective. This proves to be quite compelling in the lives of the students and in the narrative of the classroom setting, as well. These might be topics where a good thesis statement could be harvested and developed, but in the end, they are only suggestions.