My mom never makes my sister do anything..?

There's this family reunion coming up and I really don't want to go because I just had a concussion and I want to rest, but my mom doesn't care and is forcing me to go anyways. I don't think this is fair! She never makes my sister go and honestly I think she likes my sister better. My sister has gotten into a ton of trouble (including with the law) and I'm basically the perfect child, yet she always treats my sister better. I can't understand why, but once again my sister has found a way to wiggle herself out of going and she's going to a party instead. I'm stuck going with a concussion! How can I convince my mom that this isn't fair? She is ALWAYS making excuses for my older sister.