Her real name is Adora, the twin sister of He-man (Prince Adam), but who protects the planet Eteria instead of the planet Eternia where He-Man lives.
Origin of the Filmation cartoon.[]
She was kidnapped from Eternia as a child because it was said that she was destined for power just like her brother. As the plot was childish and simplified she was tricked into joining the Horde thinking they are good. But in adulthood, the He-man visited the planet, he revealed everything to her and he went there to make her a superhero by giving him a magic sword similar to his. But Princess Adora now as She-ra decided to help the planet since she helped the Horde to dominate it.
Origin in the cartoon She-ra and the princesses of power.[]
The cartoon was more complicated with the producers saying Adora was bad at first, but going through a behavior change process that involved her finding the magic sword and becoming She-ra, a legendary warrior princess, a magical legacy from Etheria. And of course she changed when she met Bow and Glimmer, two members of the rebellion (the group she joined). In this version the sword was there it was not taken by the He-Man who has not yet appeared in the cartoon.