Bondage Blog says this woman is about to get a ferocious titty-switching, which would explain the unhappy expression. “She has been watching you cut and peel a switch for her boobs, and she’s not at all happy about it!” Indeed:
"...the girls are prepared in the reformatory’s punishment room, naked, lying on their backs on special benches, bound with their legs spread above their heads, shamefully showing the two holes usually hidden..."
She looks rather defiant to me.
Defiant? Well, she looks remorseful, but still, she’s holding out.