From the experts:
Lottie is a nostalgic great-grandma name that conjures up lockets and lace, and -- like Nellie, Josie, Hattie, Tillie, and Milly -- has considerable vintage charm. A Top 100 name at the end of the nineteenth century, Lottie fell off the popularity list around 1960, but well might climb back on most likely as a diminutive for the currently popular Charlotte. It's already an amazing Number 85 in England and Wales.
There are several Charlottes who go by Lottie in kids lit, in particular in The Little Princess and the film The Princess and the Frog.
Similar feel: Lettie.