My mother passed away on Tritiya. Should I perform her Shradh only on this day?

Tritiya Shradh is the primary and most meritorious day for performing your mother’s annual Pitrupaksha Shradh. Additionally, you should perform Shradh on Sarvapitri Amavasya (the last day), which covers all tithis. Some families also perform a brief Tarpan on the actual death anniversary of the parent outside of Pitrupaksha — all of these layers of practice are valid.