She's a perfectionist and never satisfied with anything she does, even if it's as perfect as possible. She also has a huge crush on Chrom.
Cordelia is considered to be a genius who can do most things flawlessly; though she hates being referred to as such, mainly because it reminds her of being teased by her seniors, who called her a genius many times in a hazing manner. However, in actuality, it is because Cordelia realized that her comrades truly meant it, proven when they sacrificed themselves so that Cordelia could escape and thus would be their legacy. She is aware of her prodigious talents and as a result is seen as a prideful individual.