So, Nymph is one of the few ponies Shetani even kind of likes, even if she can’t admit that herself  
At the same time she’s frustrated with her and how Nymph shames her own appearance, because it’s the one thing they truly have in common. Most others see them as monsters. Shetani embraces it, Nymph disdains it.
 
Nymph eventually gets the courage to find her other mother, Chrysalis, but finds she can’t do it on her own. She knows Shetani has this fondness for deals and asks to have Shetani accompany her into the wilds in search of her. Shetani sees this an opportunity, knowing Chrysalis is a source of magic she has yet to obtain and decides to take advantage of Nymph’s need for kinship with her parent.
 
Okay she likes her but it’s not enough to turn away from power, I mean what else is there.