I posted yesterday, but I can't find my post. I'll post again. My 8 year old loves history and has since he was 6. My younger child has loved history since he was 3 or 4, probably because his brother loves it.
We don't shield them from any topic except for the Holocaust and other genocides. And that's because I can't bear to explain to my children that these acts exist. I'm not sure I can handle explaining it. That topic will wait until they're 10 or so.
My kids have done well by going to the public library. Our children's library has history books on most topics that are appropriate for their age level. They can go through and chose what they like out of the non-fiction section.
DS1 spent a lot of time with a book called "The American Story" last year. I'd be comfortable reading most of that to a 3 year old. Even though there are some unpleasant topics in there, the language is appropriate for their age level.
The American Girl series, Little House on the Prairie, and Caddie Woodlawn might be appealing to her.
DK Publishing has lots of history books.
The Step-Into-Reading series has some history books. My kids had one on the first Moonwalk, and one on George Washington, and one on (nonfiction) Balto, and one on Alexander Graham Bell, and one Lewis and Clark, and one on Pompeii. I'm sure there are more.
There's also a series called "Horrible Histories" that is written for kids. It embraces the gross stuff, though.