Just make sure she picks something up that she can actually get resources for. I.e. it isn't just an opinion paper.
Anything in particular that interests her that she has an opinion on that she can "prove" via her research?
I wont' share my 8th grade topic--it was so weak, but I was afraid about the "proof" part, that I actually did very well on the paper. But the topic itself was L-A-M-E.
(I also see no harm in you facilitating your dd's needs--so long as you don't say "Write your topic on this" and then write it for her.

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Subject areas to consider....
Travel: any places she'd like to go or see and any issues they might have for tourism, environment, govt, politics
Food: Obesity epidemic, eating disorders, healthy life style, why junk food ain't all that bad
History: Anything that piqued her interest in her class this year OR a favorite era of history that she'd like to learn more about--needs to know enough about it to produce thesis though.
Science: Same as history--kind of like a science project--without the project--again, have to produce thesis...not just a report on fireflies
Pre-teen issues: cell phones that some mentioned--some of the topics discussed on the dis recently (being picked last in PE, is it harmful or not to announce grades publicly, should cell phone usage really be restricted at school)
Hobbies: Anything she might do that is of great interest to her that she can research/explore some portion of it.
The goal of a research paper is:
1. Being able to research and back up your thesis
2. Being able to produce a coherent, well thought out, well-written paper that supports the argument utilzing the format required.
3. Learning something new or different about yuor topic that you may not have realized.
In 8th grade, they turned us lose in the library for one English class and we were to explore and find our subject--and then I think we had to complete our thesis for our homework.