Daisy's a powerful force on the field if you can make the most of her unusual special ability cycle. You can usually work it easily into mob fights, but it can be a pain when fighting heavies or in choreographed bossfights, when sudden loss of your gun is... inconvenient. Still, her mechanics are fun if not always the most effective, and she makes a good anchor for squishier squadmates.
Daisy becomes particularly useful in the late- and post-game, where her high durability lets her weather attacks that instakill flimiser heroes (*cough*Rama*cough*), and upgrades to her minigun let you keep up a steady stream of debuffs to your target. Ideal vs Pride Captains and another annoying heavies.
Daisy is unmissably recruited as part of the main campaign.