The Summer Maiden's dark (and romantic?) past with Cinder: a crack theory (no, I'm not talking about Summer Rose. This is a theory about the actual Summer Maiden)
We still don't know the circumstances of Salem finding Cinder. The only thing we can guess about it is that it was a bad situation to be in, based on 1.) the fact that Cinder was a runaway teenage girl with nobody to protect her, 2.) the fact that she says to Salem, "Without you, I am nothing," 3.) Rhodes saying that she'd always be running, and 4.) the fact that Cinder came away from the situation feeling like her own semblance and fighting skills weren't enough to protect her and make her strong, as if hard living had taught her that she was weak and needed more power.
It's also said that Cinder was a girl Salem chose- which leaves the impression that there were 3 other girls/young women Salem was considering to have serve as the vessel for the maiden powers (after all, RWBY is all about the rule of 4).
I'm pretty sure the summer maiden is headmaster Theodore's niece, the girl mentioned in his picture in one of the books. Let's say her fairytale allusion is Princess Charming. Let's say she ran away from Uncle Theodore, the only family she had left, as a teen because she felt like he didn't care about her- he was too caught up in his role as headmaster and a member of Ozpin's inner circle.
What if Salem was in contact with the leader of a human trafficking ring with the intention of finding 4 damaged girls she could groom and exploit for her master plan? She used the leader to provide her with girls, then discarded him when he was no longer useful, showing up as a rescuer of the 4 young women. One of 4 girls Salem takes with her is Cinder, and one of the 4 girls she takes with her is Headmaster Theodore's niece.
During their days in the trafficking ring, Cinder and the girl leaned on each other and feelings began to develop between them. But underneath Salem's tutelage, things start to change between them. Theodore's niece becomes increasingly uncomfortable with their way of life, while Cinder is warped into something darker. Salem doesn't tell the girls about the plan to infiltrate the academy, but she comes to favor Cinder and tells her that only one of the 4 girls can survive. She orders Cinder to kill the other girls.
Desperate to survive and also power hungry, Cinder does as she's told. When it's time to kill Theodore's niece, she feels conflicted- she did have feelings for her. But she puts herself first, and sheds a tear after 'killing' her before strengthening her resolve to be strong and not allow relationships to get in the way of her goals. She tells Salem it's done and becomes Salem's chosen one.
Except headmaster Theodore's niece isn't dead. After Cinder delt what she thought was the deathblow and leaves, her semblance- advanced healing aura regeneration- unlocks, saving her life. The old summer maiden finds the missing girl and takes her to headmaster Theodore and the authorities.
A few years pass. The old Summer Maiden dies, passing her power on to headmaster Theodore's niece. The relationship between the headmaster and his niece improve, although the niece remains emotionally scarred by her lover Cinder's betrayal. She lives her life. Then the fall of Beacon happens, and Cinder is all over the news. Fast forward to volume 10. The summer maiden tells teams RWBY and ORNJ about her and Cinder's past, and prepares to battle her former lover. She has a heart to heart with Emerald, telling her, "I thought Cinder cared about me too." How will the battle and confrontation between Cinder and her former lover play out?
If this theory is canon, it's a nice replacement for the 'Cinder loved Summer Rose' story planned by the writers. Cinder had feelings for the summer maiden, but betrayed her.
