Taking a self portrait into a mirror has been around a while. I seem to recall seeing photos of Jackie Kennedy, before she was married, that she took with a 35mm camera shooting into a full length mirror. That would have been in the 50's at least? I think it was her. It wasn't about selfies necessarily, but was about her early years before marrying. I think she did some modeling and photography work. Others may have practiced this also, especially the artsie photographers in the 50's.
Type at you later,
Dan McEntee