回複：畢業典禮想要邀請媽媽來，不知簽證有什麽準備

- your bank statement
- something to prove the relationship of you and your mom (e.g notarized birth certificate etc.)
- a letter issued by your mom's company, indicating the reason she will be on leave (to attend your graduation commencement). This will tell them that your mom has no intention to stay in US, because she needs to go back to work.

The facts that your parents are still working, sister's in college and certainly needs to be taken care of by your parents are helpful in your case.

Wish you good luck!