I feel sure that everything related in this pseudo-memoir is invented, which is interesting in itself.
It's perverse that Donner, apparently an anthropologist, presents an account of folk "sorcery"... which actually has nothing at all to do with authentic indigenous Mexican magic. Also, after reading this, I found out that Donner and three other followers of Castaneda disappeared in 1998, apparently driving into the desert and abandoning their car. The remains of one of the other women was found in 2003, but Donner and her companions have still never been found.
Against this background, Being-in-Dreaming has an overheated fantasy quality that's compelling, apart from any claim to authenticity. Donner's admittedly clumsy and repetitive writing reveals a few fixed themes that recur obsessively. Most obviously, the other "sorcerers" constantly abandon her, leaving her lonely and afraid. They castigate her for her attachment to them, as apparently this is a spiritual flaw that blocks her development as a sorceress.
Is this story actually Donner's depiction of the mysterious way that powerful, confident individuals have come and gone in her life? Her passionate and lasting attachment to Castanada, and her disappearance (perhaps suicide pact) after his death, seem characteristic of an individual in need of an attachment that transcends the possibility of separation.