The Doppler Effect is the change in frequency or wavelength of a wave for an observer moving relative to its source. It is named after the Austrian physicist Christian Doppler.
When there is relative motion between source and listener of sound, the apparent frequency heard by the listener is different from the frequency of the source. When the source and the listener are moving closer, the apparent frequency increases and when they move apart, there is decrease in the apparent frequency. This is Doppler's effect.
The wave-fronts move closer as the source and listener approach closer to each other. Thus, the observed frequency is greater than the actual. The pitch depends on frequency, greater is the pitch.
the distance is the first 80m+the second 80m she came back. So the distance is 160m. but the displacement is 0, because she came back by the direction she went.