Sister physically harassed

My sister is always close with the house help, this time it was the private driver . My sister was only 14 years old at that time. Once she was asleep in the car with the driver next to her and she felt his hand feeling her thigh very close to her crotch and she woke up and opened the car door and left. Another time she was simply walking toward the car and he tapped my sisters butt. Not long after that he quit. I was very angry that this stuff was happening to my sister but I was only a kid and I felt like I couldn’t do anything to protect her.