Answer

Nandivardhan’s sister was Princess Trishala.

In Jain tradition, Nandivardhan is known as the elder brother of Bhagwan Mahavir. Their family included:

• Father: King Siddhartha
• Mother: Queen Trishala
• Brother: Nandivardhan
• Sister: Sudarshana / Priyadarshana, according to tradition

Clarification

If you mean the sister of Nandivardhan, the brother of Bhagwan Mahavir, she is traditionally known as Sudarshana, also called Priyadarshana in some accounts.

Takeaway

Nandivardhan, Bhagwan Mahavir, and their sister Sudarshana/Priyadarshana belonged to the royal family of King Siddhartha and Queen Trishala.