Given that she is 12 its a possibility, but I would be more inclined to agree if it was a male char since males have to worry about the voice changing at puberty. But if her family knew she had a gift for sleep genjutsu, she would have started training as early as 6. so she could have perfect pitch and tone from years of practice. Not to mention at the time period this is set, all instruments were hand made. Which meant that there was no standard pitch and tone.