Life and Death or Fury.
Fury allows her to barely survive some attacks which is kind of important when you are not controlling her it also helps lower HP to 75% for other effects to kick in.
Life and Death is most optimal if you are controlling her and making sure she never gets in damage. The problem is she's so fragile that she easily gets one-shot-killed in defensive arena when AI controls her.
There's no reason to use Darting blow on her when the other two option has +3 speed and +5 speed already.
Idk if defense has a role in how your ranking will go in Arena but id still just go Life and Death. Assuming you have a +atk or +spd Linde, she gets atleast 100 kills depending on your build + life and death.
Fury will still give you over 100 wins but LaD will give you more when you are controlling her.