I worry that you are expecting perfection from your first grader in this project, rather than a learning experience (perhaps I am wrong, it is so easy to misread these postings).
If she was an adult, or even say a pre-teen, I would worry about practicing the presentation. She's going to know her content really well from what you describe, so I wouldn't worry about how well she performs in the presentation itself. If she stumbles, that's a lesson learned and perfectly acceptable.
What does she want to do? Would it help to tell her what you think (from your perspective) she still needs to do and ask her how she wants to complete the project? It might help to let her formulate the plan, you can document it for her and then help her finish it.
It sounds as though she is learning a great deal about history from this experience, even if she doesn't turn in a perfect presentation.
