Rosanna
Electric 
Machine Gun 
Attacker 
Burst 1 
Tetra Tier 5 On the Lam
■ Activates after landing 120 normal attack(s). Affects self.
Concealment: Prevents self from being the target of single-target attacks for 10 sec. Loses effect when the caster takes damage.
Critical Rate ▲ 19.34% for 3 sec.
■ Activates after landing 10 normal attack(s). Affects 2 enemy units with the highest ATK.
Dispels 5 buffs. Activates 1 time per battle.
Capo dei Capi
■ Activates at the start of the battle. Affects self.
Concealment: Prevents self from being the target of single-target attacks for 5 sec. Loses effect when the caster takes damage.
■ Activates when a Nikke is out of action. Affects self.
Frenzy: ATK ▲ 22.61%, stacks up to 10 time(s) and lasts for 30 sec.
Fills Burst Gauge by 36.54%
Vendetta
■ Affects 2 Attacker enemy unit(s).
Deals 1310.4% of final ATK as damage.
■ Affects the same target(s) when in Concealment status.
Deals 561.6% of final ATK as additional damage.
Skill recommendations
Solo Raid Usage
This is based on the top 50 players of all NIKKE servers combined. Data is from enikk.app, check their website for a lot more raid data.
Extra notes
By today's standards, a really bad kit that's just underwhelming on most (if not all) PVE content. Invest only if she is your waifu.