It is so easy to beat Sarah the Nerfkitten whether you're a gaurdian or not! All you need is a Generalists Robe from Warlics Wizard Quests with imbue with lore and a really powerful earth spell to win i suggest you are 80+ and the spell is really strong. Just imbue with lore when you put on the armour and attack. 8 times out of 10 you will win. I'm level 121 and i beat her ALL THE TIME.