British young adult adventure/mystery book featuring young girl alone, about 12 or 13 years old. She would venture into caves and various outdoor settings, pursuing the mystery or hiding from someone. At times, it seemed to be rugged terrain, but I’m not certain about the location. She would take “tins” of food and her “rug” (blanket) with her. This is how I surmised it was British.
There were at least two books like this by this author. I read them in the 60s, but I think they were written before that. They were available in my local Midwestern library, (St. Joseph, MO). There were no illustrations or pictures that I recall and, as far as I can remember, the covers were blank. They seemed to be fairly lengthy books, as well.