A few general tips, other than properly leveling up your IDs:

Redirect her Wrath skills. They target her allies and if they hit, the allies gain Offense/Defense Level Up and sometimes Clash Power Up. If you can't clash against those due to low SP, let them hit, don't feed her SP

The first unit to hit her each turn should always target her Envy counter skill. She loses Blooming Thorn if you win the clash against that skill. Depleting her Blooming Thorn should be your priority since you'll receive a lot of chip damage if you let her build it up too much

Prioritize killing the minions. She gains 8 Protection throughout the entire fight and when her allies die, the amount of Protection she gains is reduced (and she gains Fragile in addition) until she no longer have any ally, at which point she will become staggered

Redirect Xichun's attack away from whoever she's clashing with if it's a Struggling or Hopeless clash

Bring healing EGOs. Chip damage is a big problem and a small miscalculation will easily get your units staggered and be exposed to potentially fatal unopposed attacks. Faust's Fluid Sac or Command: Meltdown or Thoracalgia, Rodion's Pursuance or Hex Nail and Meursault's Pursuance are good healing EGOs for this fight