At the top of the hill, the skier has maximum gravitational potential energy. As she skies down, this gravitational potential energy is transformed into kinetic energy. She moves faster as she gets lower on the hill (ignoring the effects of friction). When she strikes the snowdrift, the backward-acting contact force on her from the snow does negative work, slowing her down.
Work Step by Step
The kinetic energy that she had is changed into kinetic energy of the flying snow, sound, and thermal energy.