Because the job of a headline is to pique readers’ interest. Ana analogous headline would be, “Golden Age film star invented spread-spectrum communications”.
"Golden Age film star" descriptor has fairly high information content because there are not that many film stars in the world. Just saying "heiress" without any additional qualifiers (unlike say "heiress to a large fortune" or "heiress to a throne") can literally mean any woman with known parents, so the information content is quite low, which is why it's weird to put it in the headline as if it's supposed to mean anything.
She was a woman at Harvard in the middle of 20th century, it's already obvious that she was rich, which once again supports my point that the word "heiress" provides virtually no new information here.
