In 1967 and therabouts, there was a period when we wore “sack “ dresses that looked like maternity dresses. We wore them short with white stockings. I remember mine and my mother in law laughing when she saw me in it saying I looked pregnant.It was all the rage with the young hippie set. And those were the years of hippie clothing, long with beads and loose fitting.
I will concede that what she might be wearing is the 70's Nancy Sinatra Boots are made for walking type of dress. If this picture is indeed real and her son was 10, it would have been the 70's.