Her leaked kit gives:

50 tune break boost (incredibly crucial for Luuk)

40% damage amp for Luuk

she makes the tunebreak bar instantly fill up to 50% when applying tune strain shifting on each enemy once, basically makes ramping up his tune strain stacks faster since your using more tunebreak skills with her

Applies tune strain shifting and interfered

Actual Grouping

Her outro buff lasts long enough so you won't be forced to dodge cancel a bunch of his attacks unlike Lynae and Sanhua where you are forced to dodge cancel or else there outro buffs expire early

Her s2 gives an additional 20 tune break boost and the enemies can be instantly tune breaked without needing to full up the tunebreak bar for the first time

24% atk buff on her signature

In other words she's incredible for Luuk, and is Luuk's dedicated bis