Full analysis
While her Skill is active she will swap to targeting based on her marks, deal 80% Linksplash damage with her normal attacks and also deal 1% of the enemy’s Max HP per attack (up to 1000 damage). Her %HP Shredding is 1% for each of her own Dummy-links, so 5% when maxed. Her normal attacks dealing only 80% Damage vs single-link enemies is pretty much entirely negligible due to her %HP Shred also dealing significantly higher damage to any enemy that would survive in the first place.
Marks are applied at the start of battle in the same order as her targeting, prioritizing enemies not yet marked. Tiebreakers for marks are random. If there is only one enemy target, that enemy will gain all 3 marks.
Her normal attacks are realtime targeting, meaning she does not lock onto targets at all. If a new target moves closer to her she will swap to them if her Skill is not active (provided marks are still alive).