To put it simply, Jayne Mansfield was the ultimate hot baby-face goddess who never grew up, and in all of her 34 years, I'm not sure she ever looked old enough to even drive. That is how I see her, as someone who never quite became an adult woman emotionally, and I believe she was never very happy even though she basically had it all and was a very good entertainer. She had a very quick comedic wit and the ability to sing and act as well.
She wasn't a dumb blonde, but someone with real talent. She was immature and never quite grew up or appreciate what she had, but if she had lived a normal, she would probably have won many awards with her comedic wit and versatility and ability to entertain people in multiple ways, but she never understood and was not able to appreciate any of that.
I haven't seen many Jayne Mansfield movies but Who Will Spoil Rock Hunter with the great comedic actor Tony Randall is the perfect example of a movie where you get to see all her talent, where she could purposely play the role of the dumb sexy blonde, which is how she wanted to be portrayed, when behind the scenes she was as smart and cunning as anyone and knew how to get what she wanted when she wanted it.
In Who Will Spoil Rock Hunter, Tony Randall plays a struggling advertising executive who needs a big client to make a lot of money for his company. And that is where the Jayne Mansfield character comes in as an incredible Hollywood bombshell who needs what Rock Hunter can give her, which is credibility and good publicity on Madison Avenue and to be taken seriously. And she and Rock make for good partners in that film.