Well, I suspect we're dealing with Storm Silverhand, since she's the sister who's most likely to be in Shadowdale at any given moment in time.  As the regional leader for the Harpers, she's probably already done everything she can to get the town's defenders in place and ready to fend off attacks, and is probably coming to us with whatever retired high-level local adventurers she could get together, ready to jump in.<br/><br/>Demi's Marshal aura means we're probably going to win initiative if it comes down to a fight.  Any chance you could hit her with a Dimensional Anchor, or some other effect to stop teleports?  If not, I could try draining out her soul, though that's a trump card I'd prefer to keep hidden until Elminster shows up.  I could also try tossing a Bestow Curse or two at her.  50% chance to lose her action each round and the -4 to several stats would both be rough effects to get hit with.