OK, without cheese tactics....
Dragons (in this game) only concentrate on one target at a time. So, spread out, use your protections and improvement spells to "tank-up", and bring in as many monsters / animals / elementals as you can...
Send the conjured stuff in first, and attack with everyone as the dragon attack your minions.
I don't see and "dispell" type spells in your mix, or arrows of dispelling, and you didn't mention what Minsc is using, if he can't hit her...
You may need to come back later, when you've got stronger equipment.
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The RudeDawg
Known in these Forgotten Realms as Perin LightEyes
and my girlfriends, Pamila and Phil