Why are "only child" girls spoiled?

My neighbor down the street , who's my best friend is spoiled rotten. She has a huge house built 10 years ago with loving parents who spoil her rotten with shopping weekly. I live in a old house with 2 bedrooms, no Air Conditioning, and currently live with 4 people in my family. She disrespects her mom daily and is only nice to her when she takes her shopping, it's pretty sad. Any advice on how to handle this? I work for my money and I'm lucky if I go shopping twice a year for school clothing.. Thankyou!