that depends on what resources you have, almost all staffs are pretty useful, and can go on anyone. if you want to use an absorb staff serra might be better as she has better resist, and higher damage. shes a cav staff so grav would be pretty effective with the extra mobility. theres always the pain double savage blow.
if you want her to use an absorb build i would go with atk/spd solo, wrathful upgrade, vantage, and miracle.
what resources do you have to give her that you are willing to spend?