*Disclaimer: This guide is a constant work in progress as I update.
In Empyrean culture, females have traditionally played an active role in fields that require combat strategies, like varying the bullet you use depending on the situation, and analyzing your combat theater to determine how best to employ traps. That may be why so many female names appear on lists of the most prominent Spitfires.
Take all that with a grain of salt and throw it into the trash. Female Spitfires are the hybrid subclass of Female Gunners, having focus in both physical and magical damage. Spitfires are known for two sets of abilities: their bullets and their grenades. What separates the Female Spitfires from the male Spitfires: their grenades. Why should you play Female Spitfires: their grenades. What Spitfires lack in terms of big guns and flashy gadgets, they make up for with their arsenal of explosives.
The primary difference between the Female Spitfires and the male Spitfires is put plain and simple: quantity over quality. While Female Spitfires lack the punch, they make up for it in the numbers... and some more. Female Spitfires are also many times more agile, being able to throw grenades while airbourne. When combined with hand cannons, Female Spitfires become one of the frequent fliers of Arad, rivaled only by Witches and other cannoneers using Aerial Fire.
If Rangers are aimed at being in the enemy's face and dealing the upfront damage, and Launchers are aimed at being far from the enemy and sniping away, and Mechanics are aimed at being away from the enemy and letting their toys do their work, then Spitfires are aimed at being a nuisance to the enemy until they mess up and punish them heavily for it. Cannon-wielding Female Spitfires may lack the incredible instant damage that other subclasses boast, but they make up for it with numerous approaches and resets to continue the slow and steady damage.
You need to maintain a passive-aggressive offense, not taking the direct approach to the enemy, but poking at them until they drop their guard. Once you have the momentum in your favor, mount as much pressure onto the opponent as you can. If your momentum wanes, go back to poking.