I dunno about that. Earlier on she seemed to have placed all the blame of the sux years squarely on MC's shoulder. All of a sudden she thinks it's Christian's fault? Seems a bit inconsistent, which is my point.
definitely not the ultimate in consistency, but on the one hand narratively it was needed, on the other hand the supreme alibi always applies: "they are young, they are in love, they behave illogically"
said in a cynical way Jaye has practically lost her brother, she makes an extreme attempt by sacrificing Christian, who is no saint anyway, in the hope of remedying past mistakes
Maybe she realized that if she never got Christian into their lives, MC wouldn't have left? I'm not saying it's all Christian's fault, but to be honest he is the fire that lit the fuse.
I don't think Christian is the cause, but they are the trigger that sets it all off, probably without him there would have been another opportunity
in the end it's just a pretext for Jaye's anger to explode and convince MC that it's better to just allign and stall
if we really want, but I'm doing fanta theory here, the blame lies with Jaye's father, who knows why MC decided to distance himself from his sister (the fear that she would be considered strange for having such a strange relationship with his brother) as children and let that separate them for years and years