How to avoid Mary Sue-ness in a freakishly "Perfect" character

No, there are plenty of author inserts who are well-rounded characters. (They're inserted by people with fairly realistic assessments of themselves.)

I'd say a Mary Sue is someone who, regardless of whatever traits he/she has or doesn't have, manages to warp the characters around her into acting more like plot devices for her story than like their own entities. If you're worried that you're writing a Mary Sue, take a closer look at everyone else. Imagine them as the protagonists of their own stories - they may not be stories anyone would be interested in reading, but that's the story that matters most for that character. If your other characters are well-rounded and real-seeming, then it's impossible for you to have a Mary Sue.

(Incidentally, the premise of your story sounds a lot like the Replica series.)

 

Googles "Replica" ,Sounds like an interesting series I think I'll look into it. This is mostly just a side plot to my story though and not the main premise.

Haha, your first sentence is what I'm afraid of but I appreciate your honesty. I suppose she can be a good (as in well written etc) character without necessarily being a likeable character which is what I'm aiming for.
Human created but not by science. Yes, she was created the age she is now.
Thank you for the suggestion I will look into the Dying Earth although most of the story is already written.

 

Yeah well the girl in the Dying Earth is only in it a small bit. She's not extremely likable (I wouldn't mind owning her, naturally) but she's well written.

I had a hunch your character was created the age she is now. If that's the case I think you're fine. Unfortunately I don't know how someone without a past or normal development would behave, but I'm sure you can imagine something interesting that will make her behavior uniquely flawed.

 

If you need a perfect character, you could make her so nice or optimistic that she becomes annoying to the other characters, especially as nobody likes it if somebody is better than them. If she's been created, you could also take into account that she probably doesn't have very much experience and therefore could actually end up being socially awkward, for example, Sheldon Cooper in the Big Bang Theory is very intelligent, yet he has no idea about how to act socially.

Just please try to avoid creating another Bella Swan