She's basically a magical teenaged spy whose talent runs In the Blood, and she's probably been chosen because she doesn't seem very threatening.
Do some research on spies and tinker accordingly to fit your setting.
Queen of Filks
Exactly what are her powers, and what is her proficiency at them at the start of the story? Is she diligent in her study of her powers or slack? What is her attitude towards her power (and let's not make it I Just Want to Be Normal)? Did she have a good teacher, or did members of her family train her in a pell-mell fashion? Does she have a particular knack in some area - maybe her illusions of other people surrounding her are middling, but she can disguise herself like nobody's business. Perhaps most keenly, does she see it as an art or a science, or both? Give her limits, give her levels to aspire to, give her struggles in her magic. Don't make it all come easily to her. Therein lies the Mary Sue Madness.
Basically, I have this female character. Her job, along with her parents, is to infiltrate an City of Adventure to leak information back to her clan. She has Glamour powers, is still in high school, there's a huge risk that she could get her along with her entire family and clan killed if she messes up, and is capable of using her powers and whatever lies she needs to get her job done and keep things under wraps.
The reader knows none of this. While there's a lot of foreshadowing and mysterious circumstances involved, its going to be a long time before people get an explanation for this character, and for the entire time she's going to be seen using her powers on people, and people are going to have some really weird reactions to her in the process.
Are there any suggestions on how to make her not come off like a Mary Sue? Maybe suggestions on how to write the Glamour?
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