Visiting for Graduation Ceremony

[tsd]

I live in India and was sponsored for a satellite MBA programme from Indiana University. I have a 10 year mutliple entry visa and have visited USA twice for my onsite studies. My graduation ceremony is on May 2010 and i plan to take my family along for the ceremony. I have my sister in law in USA who plans to sponsor my wife and kids for this visit.
Does she have to mention my graduation ceremony as a primary reason for the visit or should she emphasise on tourism as the main reason?

[kabkaba]

Don't you have sufficient bank balance? I will suggest you fund their trip, since your graduation is the purpose there is no reason why your sister should sponsor it. If they wanted to visit your sister, she may have.