On the surface, it appears that Nuwa's mutant powers induce sleep. She calls it a "tranquility wave", when describing it in lay-man's terms to Feral. Yet on a finer level, she actually turns a target against him or herself, causing a biomolecular feedback in them. She temporarily shorts out their senses, causing them to fall into a peaceful slumber
It is psionic in nature, and she does not need to make any physical contact with her target. It is unclear whether there is a physical range or maximum distance of which she can affect people. So far, she has been seen affecting a whole room of people at the same time. Whether she could affect people in other rooms that she can not see has yet to be demonstrated. She could manage to single out her enemies, while leaving their team-mates unaffected.
Nuwa's sleep inducing abilities are strong enough to affect mutants and humans alike, including individuals who have received training to shield themselves from an average psychic attack. However, she has not been in combat against other mutants with psionic abilities, and it is likely that a telepath and other psionic using individuals would be either unaffected or at least difficult for her to defeat.
Although her power is a psychic-based ability, it is evident when she uses it as her eyes become blank and begin to emit a bright green glow.