What a wonderful story! *sighs happily* I never would have thought Sinistra to be so young, and having started so recently at Hogwarts, but it makes a lot of sense and works perfectly. I so love her way to get into Snape's good graces, and become a friend, a lover, and a partner to him, and finally to assuring his survival. This is what he should have had in canon right away, someone really caring about him and what happens to him. Making all this fit so well into canon is all but easy, and you achieved that perfectly. And the part with the Celestial Code was brilliant. I love it when an author manages to introduce a new piece of magic lore and it's fitting so well into canon, and am in awe of the intricacy and logic involved of this one. And I also shudder to think what Dumbledore would have done with it - so good he didn't get his brains on!