Silda the Unseen is always running, even when Fün Tits removes her clothes at Emre's request. Her face is dirty and looks like it's decomposing. Her features are compared to Alice Cooper's as claimed by Fün. Good stuff. She was killed by Crotch Guzzler after he blamed her lack of hygiene for his failure at getting the White Phial.
The appearances are listed below in chronological order.
Fün Tits meets Silda and comments "you're gross; you're disgusting" to her face. She runs away.
S'oggy Balls was running through Windhelm meeting people when he met it. S'oggy said someone must have tarred its face and that it actually made General Burnside look attractive. They asked if it was a feral wild human and that they should report her to the animal control. They even said it should be put down. S'oggy then said its face was dirty and that someone should clean it with fire and kindness, and that fire and kindness were the best ways to clean off its face.
Cock Nibbler arrives at Windhelm for the first time. There, the first woman he meets is Silda. She immediately asks "spare a coin for a old woman, my lord?" Cock replies, "Don't you mean spare a coin for a disgusting tramp nightmare fuel?" Emre explains that this is the troll Windhelm keeps out in front of the palace.
Cock Nibbler catches Silda cooling her hands in by the snow, presumably after her hands got too hot from warming her hands by the fire.