That isn't even a full sentence on the screen?
Well, there is a semicolon. But that is indeed a somewhat long sentence. Much like H. Rider Haggard, Wodehouse is nice to read because he is (generally) easy to read. And that’s not saying because it is Dick-and-Jane simple. Big words or small words, a lot of words or few words, clarity is an art and both of those authors have that (with Wodehouse a bit more on the Dick-and-Jane end of things). If you have clarity as your scaffolding then you can mix in all kinds of interest descriptions and techniques. It will hold up.
But in that case, I do think Wodehouse goes on for too long. End it at “of valiant gaiety” and then start a new thought. He didn’t and we definitely have a run-on sentence where one is not needed for effect. Next sentence could be: “Hers was a golden sunniness accentuated by the fact that, like all girls who looked to [and verbatim from here] Paris for inspiration in their dress that season, she was wearing black.”
Or, for a more complete rewriting by your beloved Editor:
“She was a girl of medium height, straight and slim. Her fair hair, cheerful smile, and boyish suppleness added to an effect of valiant gaiety. Hers was a golden sunniness accentuated by the fact that, like all girls who looked to Paris for inspiration in their dress that season, she was wearing black.”
In the above we eliminated such baggage words as “very,” the unneeded semicolon (just start a new sentence), no need repeating “her,” and “of her body” is superfluous. “Suppleness” doesn’t need this. And we don’t need the word “all” in front of “contributed.” Tight. Tight Tight. Small point on using the two-syllable “added” instead of “contributed,” but I like it better. That three syllables is an interruption, like hitting a small pothole when you could have kept the wheels turning easier.
But it’s likely these writers pretty much were writing stream-of-consciousness stuff with not a lot of editing. And who knows what “valiant gaiety” is. I have no idea.
LOL on the First Amendment.