The only thing that gets this book two stars is that, rather than sticking to the done-before theme of teenager-suddenly-finds-out-she's-a-witch, Mlynowski switches things up a bit and gives us teenager-suddenly-finds-out-that-her-younger-sister-(and her mother)-is-a-witch.
Why did the magical powers skip Rachel, and go straight to her younger sister, Miri? Her mother explains that it could be because Miri is more mature than her older sister. Rachel demonstrates her lack of maturity throughout the book, making us all glad that she did not, in fact, get magical powers. Not that, in the end, Miri does much better, repeatedly bending to Rachel's ideas of how to use the powers. Predictable catastrophe ensues, with only a hint that Rachel has learned any of the predictable lessons about true friendship or family or the like. Maybe that's what the sequels are for, but I don't think that I care enough to read them.