Skill Build
Level 1 - Frost Bite
Level 2 - Brilliance Aura/Crystal Nova
Level 3 - Brilliance Aura
Level 4 - Crystal Nova/Brilliance Aura
Level 5 - Brilliance Aura
Level 6 - Freezing Field
Level 7 - Brilliance Aura
Level 8-10 - Frost Bite
Level 11 - Freezing Field
Level 12-14 - Crystal Nova
Level 15 - Attribute Bonus
Level 16 - Freezing Field
Level 17-25 - Attribute Bonuses

Justification: Frost Bite on level 1 is a no brainer, great disable and nice to harass with. After that Aura is maxed, it's simply her best skill. You should get one level of Crystal Nova for the slow though, it stays the same on all levels, then Bite is maxed, then Nova for the damage. Freezing Field whenever possible for some nice AoE.