*The mystery model in black is definitely NOT Geneva Mitchell
Weird to see that this came up in a new post today: just this morning, I was revisiting some of my first posts on here (just feelin' nostalgic) and as such, I was looking at this very thread! Where on page 1, I had inquired about this very thing, early in my Moronikan citizenship (in fact, that was my 10th ever post)...
And it reminds me, I do think I have since figured out who the mystery model in black is:
Doris McMahon (or McMahan, MacMahon, etc.).
She was in some Columbia product at this time (the feature CARNIVAL, the Charles Murray short HIS OLD FLAME, and I think I had spotted her in Harry Langdon's HIS BRIDAL SWEET as well). Probably best remembered as the adult "Mary Wade" (one of the two young adults who shrink) in Our Gang's SHRIMPS FOR A DAY; she's also in FREE AND EASY and Clark & McCullough's final film, ALIBI BYE-BYE.