One of my characters, Emily, is meant to be written as a character who is used to being the best in everything she does, however I'm concerned that it may cause her to become a Mary Sue. Does anyone have any tips to avoid that pitfall, and write a character that can be spoiled and talented but still have consequences to their actions?
Here is a link to her character. https://www.notebook.ai/plan/characters/349954#
Kim Possible was supposed to be "perfect" at everything she did, but she was still a well-rounded character because of her interpersonal problems, so it is possible. Neo from the Matrix was literally a Messiah character, but he still had development that made him, if not well-rounded, at least likable.
I noticed that she wants to be a role model for younger girls, which is a great motivation. Perhaps her trying to be good at everything is a way for her to cover up something about herself she isn't fond of? Or maybe in your story, if possible, she could have that one special person who she's willing to let help her, or let her guard down and be herself, flaws and all.
I would be a bit on-edge about making her this important a character. OP characters are fine to have, but usually don't take center-stage.
But for any OP character, a flaw is necessary. One I like to write in is the fact that their perfection has driven away any chance to be treated like a human being. They aren't considered people, and have few friends. They're slowly being crushed by the responsibilities heaped upon them because 'they're smart, they can take it'. Perfection is not a maintainable thing. Eventually, somewhere in the story, that character is going to fail, and everyone will be disappointed. That ego, that power, has to be broken somehow. At that point the character can be written into a more relatable person. Once you've lost the legend, it just leaves the person.
Take Arima from Tokyo Ghoul. He's freakishly overpowered. But, as we learn near his death, that power comes at the cost of a shortened lifespan. We learn that he's known this his whole life. But he dedicated his life to spoilers. That kind of dedication and love for his people is something we can understand better. Something that makes him more human (even though he technically isn't). That humanity at the last second is exactly what I mean. Though it would have been nice if we'd gotten to know him a bit better. Shame, that.