As will be noted in future chapters, Sabri and her family don't get along. With extreme prejudice. Faevras might be her older sister, but as guessed, Sabri is the smarter of the pair by far, and living on the ring has been very good for her. Pinako, who lost her son, his wife, and their daughter Winry to an accident, gently massaged the stupid out of the young elf. Being exposed to other viewpoints has also helped.
One could say Sabri has both decent scores across the board, because of her work as an artificer. And is far more socialized then most of the Drow of Erlhei-Cinlu (Yes, Sabri hails from Oerth).
From what's been presented in Canon D&D, Drow hunt down driders because they believe Lolth wishes it. The truth? Lolth doesn't care. She marks them as failed goods, and sends them back after The Test. Some drider maintain their devotion to Lolth, others go elsewhere. And on most drow inhabited worlds, the only spider girls are Drow, because the dark elves ar obviously superior to mere humans, so no mere human could ever possibly be one (they don't mention what that one time they encountered Arachne - Athena was pissed her tea was interrupted).
And then there's the subject of the transformation itself - in some literature it's a curse (most of what I'm familiar with). In others, it's a blessing from Lolth (I've seen it in a couple of places). I wish the source material would make sense. But it kind of does, since one of Lolth's forms is a Drider.
It's too early in the AM...