Presuming you are an international student,the international student advisor can be requested to write an letter addressing US Embassy in Ktm and letting them know that you have graduation ceremony on the particular date. The parent has to get all necessary documents(i.e, police clearance,property valuation,bank statements etc).Moms have better chance of getting a visa at one shot than any other relative.Forget about aunts and uncles.It is sheer wastage of money.Visa for both parents is also getting very difficult. Best of Luck. It is really a very proud moment for parents.I remember my mom crying looking at me with a cap and robe.