musiclove,
On your graduation you can invite any relatives. I had invited 3 other relatives besides my parents.
Documents required for the interview are:
invitation letter from ISO
your invitation letter
relationship document from vdc or municipality
financial document of the sponsor
property documents
Most importantly reason that the person would come back to Nepal after certain period. To support this you can include employment vacation letters, business in Nepal etc. to prove your reasons.
Hope this helps.

If your fupu financially stable (job,property) and if they think she back to Nepal . Then not issue at all. I think immediate relationship or little far not much difference. Try to show bank balance from your side too.
Good Luck.

@musiclove , तपाई को आमा बुवा लाई पहिले किन visa reject गरेको? अहिले को graduation मा नै बोलाउदा रेजेक्त गरेको हो? मेरो आमा बुवा लाई पनि graduation मा बोलाउदा visa reject गरेको थियो २ पल्ट . अनि अहिले आमा बुवा ले separately apply गर्नु भयो अनि दुवै जानाले पाउनु भयो.