You should first of all file a domestic violence case against her and her family through your mother.
FIR will not be entertained by the police and hence a complaint under s.156 3 should be filed before the magistrate.
Defamation can only be filed if she has stated something in the FIR which is false. The statements in the FIR haven't been proved/disproved yet so don't file the defamation case yet.
File a criminal complaint and a domestic violence case against her.