Sujeshtha (also written as Sujeṣṭhā) is generally described in Jain tradition as the sister of Trishala, Mahavira’s mother. In some texts she is listed among Trishala’s siblings or as a daughter of Chetaka, which would make her Mahavira’s maternal aunt. The exact lineage differs a bit between Digambar and Shvetambar accounts, but in both traditions Sujeshtha is connected as a sister/aunt figure in Mahavira’s maternal line. You can read more about these family connections and the historic figures involved in Jain narratives here