hmmm thinking about it, the most intriguing part about sayaka imo is the fact that she's deemed "hopeless" and sort of a goner, with homura telling madoka to give up on her and etc. idk, the idea that our fates could be so set in stone (well i suppose it wasn't entirely fixed: it was either die or become a witch, but still, that's no buffet) is rather interesting if not altogether the nicest or most comforting thought
wrt her selfishness, imo the message the show wants to convey is that it wasn't the selfishness itself that was "wrong", it was the fact that she was deluding herself into thinking she was being selfless, thinking she genuinely wanted kyousuke to get well, when she really just wanted him to love her! especially through kyoko pre-sacrifice, i thought the show was p clear on its stance that selfishness is a-ok, the most important thing is to be honest with yourself about what exactly you want and why you want it
back to sayaka tho, my take on it is that her character's resolution at the end, after her death, was her learning to be happy through violin guy's happiness, which were the conditions of her original wish (wanting kyosuke to be happy for his own sake, not for her selfish reasons) and hence finding peace
(IK this last part was totally garbled, if you need clarification i can try rephrasing it sometime else when i'm not running on retarded amounts of (read: no) sleep)