In Jain tradition, Trishla Mata (Queen Trishalā) is known mainly in two family relations:

1. Sister of King Chetaka (Chetak) of Vaishali

- Trishla Mata was the sister of King Chetaka, the famous Lichchhavi ruler of Vaishali. - This makes Mahavir Swami (her son) the nephew (bhanja) of King Chetaka. ( jainknowledge.com)

1. Her own sister – Sujeshtha

- Some Jain traditions mention Sujeshthā (Sujeṣṭhā) as the sister of Trishla Mata. ( jainknowledge.com)

So, depending on what you meant:

• If you meant “Trishla Mata na bhai / family side” → she is the sister of King Chetaka. ( jainknowledge.com)
• If you meant “Trishla Mata ni behen kon?” → her sister is mentioned as Sujeshthā in Jain tradition. ( jainknowledge.com)

You can read a bit more about Mahavir Bhagwan’s family (including Trishla Mata) here: