Documents to prove relationship

[immihelp]

Hi
Iam planning to bring one of my husband's relative to U.S, in visitors visa.I don't know what type of document to show for the identification of relation, because she is my husband's cousin sister.Do u know what type of document i should provide for the relationship.

Thanks,

[immihelp]

Combination of birth certificates and marrriage certificates, up the chain and then down the chain.