She wore a black moire faille (finely ribbed silk with a watered pattern) cocktail dress, with a full skirt and "angular pockets at the hipline." The bodice, while described as plain and "featuring the new plunge neckline", looks like it had a shawl collar and cap sleeves. The Mystery Woman wore a small hat of black grosgrain, perched on the back of the head, with a rolled brim and a bunch of grosgrain at the side.
Her accessories were a rope of pearls (knotted at the neck by the look of the picture), black suede gloves, and a black suede handbag with a gold clasp, and her black suede shoes were commented upon favourably as being "the low-cut classic court style which is proving so popular with dressy frocks at the present time."
The Mystery Woman turned out to be Lois Borella of South Yarra. I did a quick Google search, and turned up an inscription on a gravestone in the Mathoura Pioneer Cemetary for a Lois Borella Aslangul, who was born in 1928. If this is her, it would have made her 22 at the time this sketch was made, which seems about right. I wonder if this eye-catching young woman in her black silk dress is the same woman who died in the small town of Mathoura in NSW, aged 71, the "loving mother of Rex and Andrea"?