terz,
Women hear better/are more sensitive than men at detecting high frequencies. I'm not surprised she can hear tones slightly beyond.
The typical upper hearing range for humans is around 20kHz, (give or take a few thousand).
I spoke with the provincial nurse during my hearing test that takes place in the little sound proof booth (part of getting SCUBA medical certification over the years) and she said that discerning frequencies correctly beyond 16kHz becomes unreliable and more variable (i.e., on average people she's tested start to fail the hearing test around 16kHz).
