She starts with a nice life stat, but since she joins later her hp doesn't go up that much if you don't take the time to level. If you do level a bit you should easily get her level a fair bit above 100 which is enough to keep her alive - an auto-regen and "shield" items help greatly as well.
Phlebas the Phoenician, a fortnight dead, Forgot the cry of gulls, and the deep sea swell // And the profit and loss.
- - Gentile or Jew // O you who turn the wheel and look to windward, Consider Phlebas, who was once handsome and tall as you.
[T.S.Eliot: The Waste Land - IV. Death by Water]