How to tolerate someone you can barely be around?

Unfortunately the person is my younger sister. I love her so much, but she is someone who I would have avoided in high school: dramatic, preppy, conceited, valley girl, never does anything fun in fear of messing up her makeup or hair...etc. I can only be around her in small doses. We used to be really close but then she started high school and changed drastically as everyone tends to do. I feel like such a horrible person, but I can't help it. WHAT CAN I DO?