Did she choose NV because she’s a horse lover? I think I read every horse/dog book there was in the library at that age. I can’t remember when I read NV…what about the Billy and Blaze series? Although I didn’t read those as a child-I thought the one we recently got from the library was pretty good. I know I loved the Thornton Burgess books, the Incredible Journey, 101 Dalmations(the original) all the Terhune dog stories, and Marguerite Henry’s horse stories. My dd thought Terhune’s Lad:a Dog was too hard but after I had read many of them aloud to her, she was able to enjoy them on her own. Maybe you could find an audio version of NV first?
FWIW, I think all of mine were still doing readers at that age-we’ve used Pathway, Christian Liberty Nature Readers, and Elson readers. They branched out from there as they were ready. We did stop Pathway after Climbing Higher to focus on the other two series. (Just ’cause the budget was tight-I’d be happy to have them one day.) If you have the other Pathway books-maybe you could have her skip the one she says is easy but still have her read it for leisure.