Starlight Rose is a support variant that can provide useful BUFFS for her teammates through her Signature Ability. She excels best when used offensively, as players will have greater control for well-timed BLOCKS to activate her abilities.
BARRIER and REGEN are useful BUFFS to provide sustain, while ENRAGE provides increased damage output, making Starlight Rose an all-around great support variant for lots of different scenarios.
The ability to remove DEBUFFS from a well-timed BLOCK allows Starlight Rose to be a very useful support to counter variants that rely on inflicting DEBUFFS such as Unholy Host and modifiers from Prize Fights or Catalysts in Rift Battles.
Starlight Rose can provide ENRAGE and REGEN with BARRIER from all sources. This means that variants that can grant BARRIER (especially timeless BARRIER) such as Corrosive Agent, Snake Bite, Feathered Edges and Overclocked can benefit from having her in the bench to provide a boost in damage and sustain, which is particularly useful in Rift Battles.
Marquee Ability: Depending on how you use her, both Marquee Abilities can be pretty useful. For attacking, REDSHIFT is recommended, in case your main fighters have been defeated. For defending, BLUESHIFT is more optimal as it enhances her survivability, making her harder to be taken down.
Stat Investment: Starlight Rose will benefit from investment in ATK and Piercing to increase her damage output when used offensively or HP, Defense and Resistance when used defensively. Since her role is primarily a support, this does not matter much.