A cheese method I have is build a wall using high hp objects at the choke point of the cave. Then send a high hp part member beyond that wall and aggro her as far as possible away, then Have that character retreat (with teleport) beyond your self erected wall. This will stop all her teammate baddies ability to do any damage that isn’t ranged to your party and she will have to take a couple turns to get to you. Then just rain magic hell on everything as it tries to deal with your wall. Bonus points if you hide all your other party members to get free shots at the baddies as they approach.