Not this again...
I feel to come to this conclusion, you'd have to lose all nuance to come to this.
Remember, the main reason she even considered this was due to Himuro's speech snapping her out of the cycle. Note the "Leave me alone for a while!" in that chapter. This is her attempting to come to grips with the situation she's in, and the way that occurs is not by continously staying in it, at least in her mind, that and also a misguided feeling Karipi would be the one to guide her out of the cycle, mostly due to high emotional vulnerability at that stage and as well Karipi being the only one aside from her sister to (seemingly) show a care for her.
Her world came crashing down, and Karipi took full advantage to lure her in, cant really blame her for falling into that. And alongside this, Kira threw the cycle back at her when she reappeared at the door, mind you, while Sera is still attempting to come to grips with her feelings, and that lead to eventually breaking the ceiling on the whole matter as a way to finally stop the cycle. Obviously, I dont blame Kira for coming over, nor knowing she'd likely indirectly cause that mental torment, she just wanted to be with her sister at all costs, but it was easily, wrong place, wrong time and it backfired.
I wont say Sera had no fault at all, but to say she deserved it is such a black and white way of thinking. Im more of the opinion she made mistakes while clearly not being sound of mind, and thats just typical when one is emotionally vulnerable.
You act like knew she was a manipulator... obviously we do since duh, we reading, but she likely wouldnt pick up on signs due to the current sister situation overwhelming her emotions... no duh thats gonna lower defenses.
I feel stories like this are not your forte man.