At first she was only pretending to be a soldier in a noneexistent Rebel army alongside Pearl, like a game, to get Gems to leave Earth. Already that’s altruistic, basically throwing away what she thought was her only chance at being loved or respected again all to save some flowers, birds, and Gem-like animals who smiled and waved at her.
Had it been a success she’d have left Earth and put it behind her.
The fake Rebellion became a real one because she saw how much Pearl loved pretending she was Pink’s equal, creating a narrative in her mind that it was real. Then immediately after telling Pink this insisting “No, I must be broken to be having thoughts and feelings of my own, of belonging with rather than to you. Please kill me, and ask for a new servant.” Which obviously fucking horrified Pink, who was already traumatized from losing Volleyball and realizing how fragile other Gems are.
Pink, who hated herself, immediately fell in with the idea of “noble renegade Pearl fighting for Gems like herself accompanied by a Rose Quartz to bear her shield”. Then this start to romance between them was followed by almost forming Rainbow, a new experience of sharing yourself that she had been told was impossible.
Followed immediately by finding Garnet, a Gem who was choosing to be something entirely new that was not one of her components. Someone that Pink would have to protect, since it was her duty to find and destroy Gems exactly like that.
In one day Pink went from queen to follower, from playing a game like a Scooby Doo villain in a mask to scare away Homeworld to being her own arch enemy.
According to Homeworld, Diamonds were perfect and Offcolors/Rebels/Noncomformists less than nothing and had to hide to survive. But as far as Pink was concerned Diamonds were just dumbass powerful Gems, she herself was less than nothing, and as long as she hid her true self away the great beautiful Gems she surrounded herself with would love her.