Don't cripple your champs by using complete sets by any means. Get the right stats from your items instead. If you can complete sets that way, great. If not, prefer the right stats over completed sets.

Important stats for her are accuracy to land the freeze, def and hp for survivability and speed to get more turns during the fight. Good main stats could look like gloves def%, chest hp% or accuracy, boots speed. Substats to look for on all items: accuracy, speed, def%, hp%.

If you have a big enough item pool to meet this requirements for her gear with completed sets, I would chose Perception or Accuracy.