What if my sister is being held responsible for a loan she didn't take

Me and my friend live in Australia. My friend is going to India and she need Indian Bank account no. to get some money(50000) transferred from one of her friend in India. I gave my sister's account number, money got transferred from U.P to Delhi Account and I gave dollars to my friend here in India. Now 3 months later a legal notice came at my home in india in my sister's name(it was regarding that money transferred) but we refuse to accept the notice. The person who transferred money from Uttar pardesh to delhi wants his money back or else he will fill law suit against my sister. What we can do about this situation?