In a case like Duncan, if you have gained a new warlord it would be important to locate and remove all blocks to him acting with less that 100% loyalty to you if you want to trust his judgement and use him as soon as possible, and Jillian needed an experienced Warlord (here's a thought - that might have been the primary objective in attacking Jitterati). ...
The attack on Jitterati got Jillian several things;
- besides for the warlord,
- eliminate a nearby side and gain their resources and territory, thus buffering the core of FAQ even more
- alliance and help of the mountain giants
I suspect that Charlie scouted the idea out and suggested it to her, having already set her up with Vanna. He knew what she could do.
And we've believe that Charlie is behind the issue of the missing gobwins, a similar issue to the mountain giants.