Marilyn Monroe was not a Sagittarius.
It did rule her 5th house though.
The ruler, Jupiter, is conjunct her Moon in the 7th house: the fact MM was so 'open' was part of her appeal because it made her accessible to millions. The reason for this openness could maybe be defined by this quote,
"I knew I wanted to be a star. Not because I was beautiful or even talented but because I had never belonged to anyone." Marilyn Monroe
She made the yellow bikini herself. It was scandalous to wear a bikini that was so revealing. Usually, it was a rule in the '50's to cover the bellybutton up. Marilyn's Monroe's daring attitude towards her body and sex was a theme throughout her life, beginning at puberty where she covered up her poverty and competed with the other girls who had nice things by standing out.
The photographer, Anthony Beauchamp, would go on to ask his other models to wear similar bikinis.
What we are seeing in the above picture, is just one of thousands of photos where we are seeing the beauty of Marilyn Monroe that transcends physical beauty because the psychology is so fascinating.
In my opinion, she was an undiagnosed manic depressive; a grieving artist who gave everything she had to her art. Unfortunately, it was a doomed mission, she was fighting on empty because she did not have the tools to heal herself and was born in a time that could not understand her. The strength of character it took to fight the good fight under those circumstances cannot be more emphasized when trying to understand the essence of Marilyn Monroe. Saturn at the bottom of her chart and South Node in Capricorn 6th house do not exactly describe a comfortable existence, but it gave her the drive to get out of bed every morning. Marilyn Monroe showed up to her work and gave it 100%.
The infamous lack of time-keeping later in her career was caused by a sleeping pill addiction and declining mental health but that was genuine and not to be confused with laziness. There was probably some rebelling against the patriarchy of the Hollywood movie studios too, along with genuine fear of not being good enough (a fascinating, complex creature with multiple reasons for her actions).
Then there is the tragic side of Marilyn Monroe. The twin she did not show to the world. She gave it her all when in manic mode and the crash was inevitable. Once she had finished work, she did not have the inner stability to cook dinner or ground herself, instead she would take sleeping pills and sleep, not wanting to face the intense darkness that would have come.
Here is a professional photo by Richard Avedon which captured the inevitable fall. Or maybe it is simply the real person behind the character, the abandoned, Norma Jeane.
“For hours she danced and sang and flirted and did this thing that’s—she did Marilyn Monroe,” Avedon said later, adding that the white wine helped things along. “Then there was the inevitable drop … she sat in the corner like a child, with everything gone.” And he clicked his shutter once more. “I wouldn’t photograph her without her knowledge of it. And as I came with the camera, I saw that she was not saying no.” Richard Avedon (https://nymag.com/news/features/31523/)