I could read Hildegard Frey’s Campfire Girls books all day, judging by the two I’ve read via e-book. As you remember, I had a "corking good time" with The Campfire Girls Go Motoring, as much for the portrait of automobile travel in 1916 as for the mystery involving the separated car and the mysterious girl they pick up. The Campfire Girls at Camp Keewaydin which I just finished, has no such compelling narrative, but I found it interesting just the same. (Yay! There's another one waiting at blackmask.com!)
It is mainly the story of "Agony" (Agnes), a nice, honest, athletic girl who longs for popularity. Innocently, she is caught up in a lie, which she perpetuates because it gives her the longed-for popularity, but it weighs upon her soul all season and eventually comes to a bad end, from which she emerges truly "sad but wiser." It's one of those stories where you keep mentally advising the lead character to do something to get herself out of the mess, because except for this one fault, Agony is really a nice kid.
What is more fascinating in the book is the glimpse of 1920s girls' camp life--canoe trips, swimming contests, practical jokes, good and bad councilors, crafts, plays--especially the idea of "crushes." From the other books of the era, even boys' novels, it was apparently very common in those days for younger teens to hero-worship older ones. Oh, this still happens today, but the "crushes" are described in the books then in a way that today would smack to most people of lesbianism and homosexuality. Intimate sharing of a sleeping bag with a special friend is made a point of, or sharing glances with a fellow girl or boy. However, in those days it was all quite innocent and people would have been shocked and outraged had an accusation of homosexuality been leveled at these "crushes." It was considered natural for a girl to idolize an older girl who was popular and pretty, or a boy to admire an older companion who was good at sports or in leadership.
Funny how today we can make admiration and friendship into something that many people consider unsavory--and into something sexual when it's not.
Anyway, here is Jo Anne's Girls' Book Web Page, which has short and long reviews of different old girls' series books, plus a few in-general essays about them at the bottom of the page.