It is not known if the woman in the photo knew her picture was being taken.
After a barrage of criticism Mathers apologised and took the post down.
I can't imagine what possessed her to take a photo of a naked 70-year-old woman - let alone think it was wise to put it online.
Los Angeles prosecutors have charged Mathers with invasion of privacy - and so they should.
What a gross breach of this woman's privacy.
When we enter a pool or gym changing room we shouldn't have to be afraid that someone will take a sneaky pic and reveal us in all our glory to the online world.
Earlier Mathers said she posted it accidentally. But she didn't accidentally take the photo and that was where she first went wrong.
Before you load up your latest Instagram, take a moment and think about what and who you're portraying and if you'd be happy to be snapped in such a position.