I heard that Lindsey and Carol Ann kept to themselves and just hung out in the hotel and stuff, and didn't go out partying like the rest of the band. They were a low-key couple...so Mick must have been sneaking her cocaine
The scene in some video, where Richard Dashut makes fun of Stevie's ballet moves, he later says something to her like, "Don't worry, you won't have children!" and she looks really hurt. One can only imagine what had happened at that point...