How can you easily defeat Umbra

If you have a Nord character, you can use Nordic Frost to seriously hurt Umbra. Better yet, if you have the Lover star pattern, you can paralyze her, use Nordic Frost, then finish her off with mellee weapon strikes. If you don't have a Nord, become the Arena Grand Champion, sell the Raiment of Valor, and you will have enough gold to buy the Apotheosis, a staff that does 33 damage in frost, shock, and fire. Slide the difficulty bar all the way to the left, and Umbra will die in one blast.