Try using a shadow potion and waiting for her Blind spell to wear off, then attack. If you can not see her (ie the egg-shaped shield), you can not hit her (except with area effect spells which do not need a target, like Hell Spikes, Poison Cloud, Elemental Hail, Deadly Disks...).
If you drink a shadow potion and use your spin attack near (but not directly on) a creature, you will hit it without turning visible.
