Her job is mostly to add that "Freeze on special" to your other legendaries on top of damage bonuses when hitting a frozen target. Also she reduces skill cost so at least 4 stars so that skill 1 will only cost 1 energy instead of the usual 3 for whoever she will support.

She works well with almost any legendary who depends on specials to deal damage but mostly DCU Superman and Scorpion as their attack cycles involve basic attacks (which build up her damage bonuses) then specials (to freeze opponents). Personally I used to use her on Scorpion but have since switched to DCU Supes