I found her three times.
Yup, I found her. The ninja was a bit tricky to find with the music distracting my senses, plus she moves around each time you play, but there she was the first time in the 18th tree to the right of the wind turbines closest to the nearest hill. The second time through she was hiding in the 2nd window on the red roof behind and to the right of the church. The third time she was behind the lamp post in front of the bicycles. I have to admit, this would be an incredibly difficult game for anyone who isn't a ninja themselves, so maybe you'd be best to tone it down for the general public, maybe get a less experienced ninja instead of the full ninja you had for this one, because I'll admit she is quite professional in her sneakiness.