1. As per the certificate, sh was an adult when she had married her husband. So, it is a legal marriage,
2. Your Cousin sister has married the person whom you are calling a criminal but she has willingly married him,
3. It is only she to decide whether she will continue to have matrimonial relationship with him or not,
4. If she decides to terminate her matrimonial relationship on valid ground (like cruelty, criminal activities etc.), she can file a divorce sui after one ear f completion of her marriage.