You can do this using whatsapp Restore function .
1> you need to get hands on her phone .
2> you need her phons memory card and sim card .
2> obviously phone is locked .
3> when she goes to washroom or sleeping get her memory card .
.
4> turn of you internet connction .
5> uninstall whats app
6> reinstall whats app
7> copy SdCard/WhatsApp/Media to your phone
8> not out her sim card in ur phone .
9> open whatsapp .
10 > job done
Whatsapp will ask you to restore messages Ho it happily and see with whome your girlfirend or wife doing chat .
