What's this "Jl. Sg." appended to a name in the Social Register?

Screenshotted from the (fictitious) "1929 Social Register" in the opening sequence of the film Down to Their Last Yacht (1934).

"Miss Linda Colt-Stratton" I get, but what's the "Jl. Sg." after her name?

My impression from some very cursory Google-Booksing is that typically the Social Register would contain earned titles such as degrees ("M.Sc.", "Ph.D.") or I suppose military ranks, but even if Miss Linda Colt-Stratton were a sergeant, I still don't understand the "Jl." part. Vice versa, I've found "Jl." used as an abbreviation of "July" in one place, but I don't see how that would explain anything, either.

Theories which additionally explain Mrs Geoffrey Colt-Stratton's "Cda." suffix will earn bonus points. :)

The abbreviations are almost certainly club references or academic affiliations. I'd go with "Junior League" for Jl, but it would be a guess. Sg. could be local to wherever this SR is from, or it could be made up, seeing as how this is a fictitious register. Cda appears to be Colonial Dames of America. Google has published the 1909 NYC Social Register, and the abbreviations used in it, including Cda, are listed at the beginning.