[SixOfSpades]

If no AoE spells can cross the "wall," then pretty much the only option is to have a party Sorcerer (or Mage, if you've done WK) continually casting Wish. Is it me, or should Weimer have noticed something was slightly amiss when Improved Faldorn became more difficult to beat than Improved Irenicus?

My alternative plan of attack involves Jaheira sitting in the Sphere until Faldorn's Nature's Beauties and FireStorms are gone, and then casting things like Insect Plague and Storm of Vengeance on herself--they might not make it out of the Sphere, but it's worth a shot--and then summoning up a storm (Conjure Animals, Greater Elemental Summoning). The Summons should appear next to Jaheira if she casts the spells on herself, and since they're not in the Sphere they should be free to attack.

I strongly doubt that Otiluke's Holds its target--but if it is, you can always use Free Action.

Of course, I can't speak with certainty on this, not having put any of it into action--but I will. My Nalia is currently Level 16, have patience.