Attack drives the damages of her normal attack (the firebolts) and Will sets the damage output of the abilities.
She doesn't use the staff when in her fire form, she uses the two pieces of equipment at the far right of the screen. And vice-versa for her human form.
Ah, gotcha. Makes sense now. So if I'm staying in fire form then I shouldn't bother much with the staff, just the accessories. I thought it might be the staff, so I unequiped the staff and looked at the Attack DPS and Ability DPS, but the difference in not having the staff didn't change the way I would have expected