The excerpt is from 木乃伊の口紅 by 田村俊子, not 砂がき by 竹久夢二. Also, the reading of 砂がき is "Sunagaki", not "Sagaki".
田村俊子 木乃伊の口紅
竹久夢二 砂がき
若い女が二人して淨瑠璃でも語つてゐる樣な風をしてゐる means "two young women look like they are performing jōruri or something", not "two young women are talking as if they are performing jōruri". 淨瑠璃 doesn't refer to 人形浄瑠璃 here. There is no doll. They are just telling/singing a story.
その片
々の女 must be a misreading (or miswriting of the writer herself) of 片方.
上の看板に、肩衣をつけた女の身體からによろ/\と拔け出した島田の女の首が人の群集を見下してゐる樣な繪がかいてあつた。
ろくろ首 is a picture painted on the sign board. There are two women on the stage.