Rupee

In Iron Code lineups, she's a Burst 2 who supports buff stacks and crit through Prize1.
Mileage2 and Single PaymentB can raise her own and allies' ATK, but she isn't a main pick in recent Raids or bosses.
Since Blanc and Noir, the general Burst 2 slot is better filled by alternatives.

Every 30 attacks, Mileage2 stacks her own ATK, and every 100 normal attacks, Prize1 raises Iron Code allies' buff stacks and Crit Rate.

When Mileage2 is at max stacks, Single PaymentB damages enemies within attack range and briefly raises all allies' ATK. Her Burst cooldown is 20 seconds.

Keep sustained fire going so Mileage2 stacks build every 30 hits.
Bring Mileage2 to max stacks before bursting, then use Single PaymentB.
You can leave sustained fire and stack upkeep on auto.

There's almost no evidence of her being paired in main squads for recent Raids or Arena. Past lineups built around Iron Code units and Liter are rare in the current meta.

For Prize1's 100-shot condition, use reload (Resilience Cube) or ammo (Bastion Cube, Wingman Cube).

Fit the remaining lines, such as ammo and crit, to sustained fire and Mileage2 upkeep. If she grows too strong, she can easily take ATK buffs meant for the Burst 3 DPS, so adjust according to squad priorities.

If you don't plan to use her, leave her at 1/1/1. When raising her, tune her own ATK with Mileage2 and raise Single PaymentB's ATK buff. Prize1 only matters much in Iron Code lineups.

She isn't a main Burst 2 for Solo Raid, regular bosses, or Arena. She's only occasionally used in old lineups bundling multiple Iron Code units or as ATK buff support.

At max Mileage2 stacks, her own ATK rises greatly.
Single PaymentB deals area damage and gives all allies an ATK buff.
Prize1 supports Iron Code allies with buff stacks and Crit Rate.

She's almost never seen in recent Raid and Arena lineups.
As a firepower type, overinvesting in her makes it easy for her to steal buffs meant for the Burst 3 DPS.
She's outclassed by general Burst 2 units such as Blanc and Noir.

Rupee: Winter Shopper is an Electric Code Burst 1 Defender with a different role. Winter Shopper tends to receive lower performance ratings.