In this first image, I had her lay down in the shade with the sun slightly behind her. The background is too bright and the light coming from behind makes her face dark in some places.
In the second image, she is in the same position but I moved her so she was facing the opposite direction. Now the sun is lighting up her face instead of making weird shadows.
Always play around with which direction you want your subject to face. Light can be so unpredictable that many great pictures can be accidental. You never know exactly how the light will look on someone, so finding that sweet spot takes practice and lots of moving around.