In this interview, Elizabeth Wein says:

I drew very much on my own background—and my grandmother’s—for creating Rose. It is really the first time I’ve ever done this. Not only did I use the Pennsylvania Dutch background as a cultural reference point, but I actually set Rose’s hometown in my grandmother’s hometown—Mt. Jericho is Lebanon, PA, and Conewago Grove is Mount Gretna. I also have a specific airfield in mind for Justice Field—Reigle Field in Campbelltown, where I got my American pilot’s license. It is still family owned and first opened as a civilian airfield in the early 1940s.

(About 50 seconds into the Mt Gretna video are pictures of the lake, which kind of rips my heart out a little bit to see because of The Lake Story.)

And here’s the website for Reigle Field, which is lovely, but, but, THIS VIDEO:

And of course we can’t forget the Hotel Hershey. I am probably stupid, but I did not realise it only opened in 1933, which means it was still pretty new when Rose was growing up! (I have no sense of time. I really don’t.)