It depends.

The only thing that differentiates a Canon Sue from a Mary Sue is the type of fic they reside in. There are tests out there online to tell if your original character is a 'Sue.

One glaring sign your character might be a Sue is if she and the hottie who've been lusting after one another for an entire novel find out they're actually brother and sister at the end, and in the next novel of the trilogy they spend pretty much the entire thing drooling over one another and not one single person around them slaps them up and says, "Hello, incest?". If, when the third novel opens, she's having a Sad Moment because *sniffleweep* her brother is acting like he has no feelings for her anymore and she was just So!Sure he really did and now she feels like a knife has been driven through her heart. It only took him the entire last novel to finally say, "Yeah, we really should cool it" and then he had to go and ruin it with body language and actions and tone of voice that made it abundantly clear he was doing it only out of extreme reluctance. I have no idea how much incestuous lusting the third novel of Cassie Clare's trilogy is packed with, but considering she remarks that the character on the front cover of Novel three comes between Canon Sue and her Incestuous Lust Interest, I feel secure in saying there's plenty to be had and that it won't turn out to be incest after all because *gaspsurprise* he's not actually her brother. He was confused/switched at birth with her real brother so it's perfectly fine for them to be shagging like nymphos deprived for a year. *rolls eyes muchly*