Woman sunbathing on a beach - 1968

A lady sunbathing on a pebble beach sometime in 1968.

I hope I'm not being impolite to say that this lady is of more mature years. In order to get the most exposure to the sun, she has lowered her straps and lifted her dress up to expose a lot of skin - I wonder if she expected her picture to be taken? I also wonder if she knew the photographer or if this was a candid picture?