Unauthorised access to gmail id &changing the password by Husband and Texting wrong whatsapp msg

My sister marriage happened on May, 2017 ,My elder sister has made a domestic violence complaint to CAW, DELHI WOMEN COMMISSION, AREA POLICE STATION against her Husband and in laws family. She has some proof with regard to her complaint saved in her Mobile Phone and some screenshots of bad & wrong whatsapp msg that her husband was sending. Therefore as she think in order to Clean those proof against him, My elder sister's Husband has unauthorisely access the personal gmail id of my elder sister and changed the password of the gmail id of my elder sister. He did not have the password of the gmail id. But the Mobile no, registered in the gmail id was in husband name. He used that mobile no. to unauthrisely change the password of gmail id of my sister. Also He has many times sending whatsapp msg, in one of them he claims that my sister has gone under abortion two times on saying of her mother. This is completely false and ridiculous to hear. My sister can proof this by medical examination if needed. But the point is......what legal proceedings &: under what IPC or IT ACT he can be booked if found guily of changing password unauthorisely/hacking the gmail id. How can it be traced that how he changed the password of the personal gmail id of my sister? and By sending this abortion whatsappmsg (we have screenshots of that msg) Do this is a case of outraging the modesty of a woman? or under what IPC he can be booked???