1) if your sister has issued cheque then in case cheque is dishonoured then complaint under section 138 Ni would be filed against her punishable with imprisonment for upto 2 years
2) if sister has issued blank signed stamp paper then any creditor can fill in details and sue her
3) your sister should file complaint under 498A against her husband that he has forced her to issue cheque and sign on blank stamped paper
4) also divorce her husband on grounds of mental cruelty