Dani Mathers posted the photo to Snapchat along with the comment: "If I can't unsee this then you can't either".
She says the photo was meant for a friend, but instead she posted it to her thousands of followers.
Police have now tracked down the victim of the attack, believed to be in her 70s, and say the woman is more than willing to testify to bring Mathers to justice, TMZ reports.
Mathers could be charged with dissemination of private images, which has a maximum sentence of six months in jail.
The 2015 Playmate of the year has already lost her job as a radio show host and been banned from the LA Fitness gym where the incident took place.