D&D 5E Daggerford plots

OK, so I'm running a home-brew campaign centered around the Daggerford area. I'm trying to use all of the post-Spellplague sources at my disposal to create an interesting campaign. This includes the D&D Next adventures from the area.
With the SKT, a new piece of information was revealed.

Pencheska from Scourge of the Sword Coast was alive and had taken over the form of Lady Morwen. The real Leady Morwen is trapped in Cromm's Hold. The Baroness Cromm has been promised the Dukedom when Pencheska's plans are done.

So.. since one of my players choose Faction Agent Lord's Alliance as a background, I want them to stumble upon this plot at some point in the campaign. But.. I'm not really sure what Pencheska's plans are. She has moved her way up the ladder so to speak, so maybe it's as simple as taking over the form of someone higher up the food chain in the Lord's Alliance? Other suggestions?

Also.. I cannot see a reason for why the real Morwen is kept alive. Unless Baroness Cromm keeps her secretly alive in case Pencheska betrays her?

I find it weird that Pencheska is still alive in the material plane, as the last time we see her is in the Doomvault in the final D&D NEXT adventure Dead in Thay, in which I assume most parties killed her and send her again to the lower planes? I mean, why would be there again? Don't fiend have like a period of some hundreds or year of something that they cannot return to the material plane or something?

They return at the speed of plot.

Sometimes they're barred from returning for a whole century, sometimes they're back twice during one and the same lucnh break.

anyone?

Daggerford is a sleepy little town often ignored by its larger neighbors. It is the perfect place to carry out a nefarious plan without being noticed. In short, there is so much potential here, I don't even know where to begin.

1. Pencheska is depleting the treasury to fund...
a. ...an expedition to the Crumbling Stair to retrieve a demonic artifact.
b. ...opening a portal to the Nine Hells.
c. ...a goblin army, which will soon march on Julkoun.

2. Morwen is being kept alive because...
a. ...you never know when Pencheska might need information from her.
b. ...she is being held ransom.
c. ...a Zhentarim agent is infatuated with her beauty and can't bare to kill her.

etc.

The proximity to Dragonspear Castle is also really easy to tap in to. Depleting the treasury and using her status as an Lord's Alliance member to fund a re-opening of a portal at Dragonspear Castle sounds like a good plan!