And laid her soiled gloves by […] (12)
Why are her gloves "soiled," or dirty? Sure, it's raining outside, but this is an interesting, and perhaps telling, detail to include. Perhaps the "soiled gloves" are somehow symbolic of Porphyria's "soiled" virtue or reputation.
[…] untied Her hat and let the damp hair fall, (12-13)
We pointed out the importance of the word "fall" in "Symbolism, Imagery, Wordplay" – it could suggest the Victorian idea of the "fallen woman," who has "fallen" from virtue by having sex outside of marriage.
And made her smooth white shoulder bare (17)
The "smooth white[ness]" of Porphyria's shoulder contrasts with the sin she's committing by visiting her lover.