In 1958, another Kryptonian craft crashed on Earth. Superman was able to beat the authorities to the crash site and rescue a teenage girl who turned out to be his cousin, Kara Zor-El. She was the last survivor of Argo City, which had remarkable escape the destruction of Krypton by becoming a hastily improvised generation ship, only to have his people succumb to radiation poisoning over the course of the next 30 years.
The comics depicted Kara being placed in an orphanage by her bachelor cousin before being adopted by the kindly Danvers couple. In reality, as in certain “imaginary stories” of the day, Clark Kent was married, and he and his wife, Lois, eventually adopted the girl. Through there government connections, they were able to obtain for her a cover identity, Linda Lee Danvers, an orphaned child who had died. Her Kryptonian heritage was thus safeguarded and kept hidden to allow her a normal childhood, as Kal-El/Clark had had.
But Kara didn’t arrive as an infant. Adapting to life on Earth wasn’t always easy. She had to hide you she was, and she fought against the foreign culture of her adopted world. Kryptonian society had a much greater degree of gender equality than Earth of that era, even in the home of assertive investigative reporter, Lois Lane, and the so-called Man of Tomorrow. Kara defied her cousin and guardian and began adventuring as Supergirl. Superman was eventually forced to publically introduce her.
Kara left home at 18 for Stanhope College and didn’t look back. She got involved in movements for social change: the civil rights movement, protest against the Vietnam War, and the women’s movement. She largely abandoned her superhero identity. In the late 60s, she was living in San Francisco and working at KSF-TV as a camera operator and freelance journalist. That was when she wasn’t involved in activism. She joined the women’s group Sudsofloppen and other organizations, and participated in protests from picketing to guerrilla theater under an assumed name, Karen Starr. It was at one of these protests that she showed up in a cape, white swimsuit, and blue go-go boots. The police and others trying to counter the protesters didn't know what to make of her. The press started calling her Power-Girl, much to her irritation.
By the mid-70s, she was in New York City and took a job as editor of Woman magazine, owned by J. Jonah Jameson. Jameson disliked the “women’s lib” approach the previous editor had taken. He wanted something useful for women: diet tips, fashion, recipes, the like. He was going to be disappointed. The magazine was also provide coverage of a new superhero, Ms. Marvel, who espoused the magazine’s feminist viewpoint. A superhero who was none other than Linda Danvers.