@Lord WyrmSpawN
I wouldn’t say self-confidence, more like lack of discipline and lack of social conscience, which seems to be the case after watching A horse shoe-in.
If she had quality features, I would understand why so many people like her. The main character from Great Mouse Detective has a huge ego, but at least he has impressive skills that makes you admire him, like detecting clues, nice deduction skills and he plays the fiddle quite good.
In comparison, Trixie has some visual tricks from Boast Busters, the teleportation skill that got worse every time she uses it, but not much else.