Not sure how to interpret the font used at the end, but Miriam looks more like a victim of Pink Clouds here than someone falling asleep. If she's aware of what's happening in Erin's dream, perhaps she's somehow experiencing Jacqui's dream and being affected by the perfume therein. But I think it's more likely that some pre-programming is taking effect.
If there is a Pink Clouds element then that does suggest Yves/Sawyer/Q. But if there isn't actually any physical source of this smell, then it could be anyone who has triggered one of Miriam's memories of being subjected to Pink Clouds, say.
Whether anyone is aware of Miriam's special nature (other than Jakob, who appears to have been involved with her since before she was born) is another matter. But we did see Sawyer and Hans exiting the antiquarian bookshop in 121 with big packages under their arms. So Sawyer (or Hans) might possibly have an interest in some kind of arcane knowledge.
Another possibility? Well, there are lots, obviously (Aiken farts sleeping gas?). But maybe all of the women who've inhaled the new perfume are going to start falling into a catatonic state.
It would be nice if Miriam were to enter the dreams of the other women. Perhaps this is part of the arrangements that have been made by Erin's doctor regarding the other woman.