Can you PLEASE help me decide what to do?

Here is my dilemma. Today I was offered VIP tickets to watch S. Williams, J. Isner, Melanie Oudin, and S. Querrey play at UGA. The tickets are worth 70 bucks. I will also have the chance to meet each player at a before match lunch. These players are the top American tennis icons. To an NFL fan this would be equivalent to going to see your favorite team play their biggest game of the year and meeting the players. It is a very unique opportunity. The problem is that attending this event will cause me to miss my older sister's college graduation. I am 16 and she is 21. She is not graduating from a special college and she is getting a business degree. The entire family will be there, no one is coming from out of town though. My mother is leaving the choice up to me and I have no idea as to what I should do. My sister never comes home and if she does she comes to mainly see her friends. I mention that to show what kind of relation ship we have. WHAT SHOULD I DO?!