I can understand removing the respawn since, even if it HAD been intended, the current implementation results in lopsided outcomes depending on how quickly the player gets to her.
Respawning those books based on some other, fixed factor - like every certain number of star stones discovered - would avoid that. (No matter when you first make her available, she'll only offer N copies over the course of the game.)
If they're meant to be a one-time purchase though, I do feel that it would be more appropriate to have one for each PC, or perhaps a single book that applies the benefit to both when read.
