The first 6 star SMG, and oh boy, she deserves it. As long as the damage isn't so overwhelming that it can kill her dummies outright, she has a chance to negate the damage. The chances increase if the enemy has more debuffs or has Marks of Vengeance on them, which immediately makes her a good pair with M4. Also the Sop doll is cute and comes with weird features. This is literally Sop's fault.

A high class SMG that you get for free (and even better, starts at lvl90 with 5 links when you get her now) providing well balanced stats, and a very powerful tanking skill. -Enemy ATK power (nevermind her own +evade!) that goes off in the first 3 seconds, makes tanking the initial contact much easier, and is usable even from an off-tank position.

Can easily be a main or off-tank, combos well with UMP45 defensively (though she doesn't offer much for DPS), and passable tile buffs (that doesn't clash with anyone's, but they're not amazing either). Her main weakness is she has very bad uptime (5/12) compared to some other SMGs, but the quick startup and utility (and the fact most fights are short anyway) make up for it.

Did I mention you get her at lvl90 and 5x linked? That's REALLY helpful if you're starting out.