Can I also get a tldr on why people want to go to stirland again?
This seems to me to be the most boring of the options available.
Multiple reasons:
A. You know that whole worldbuilding tidbid with Kasmir and the Old Gods of swamps and fens? Guess which project will have Mathilde learn more about it?
Also, who knows what else obscure mysteries lurk in that forgotten realm.
B. Opposing Sylvania was Mathilde's baptism of fire. She's a born Stirlander and the right hand of the Hunter-Count.
Campaign against Drakenhof, the chain of events there culminating with the destruction of Castle Drakenhof, not only created her legend but it also in many ways defined her as a person.
Her love of dwarfs even stems from those events.
Why does this matter?
Because as her later actions show, Mathilde cares about what happens in Stirland and Sylvania.
And the job of pacifying Sylvania, Abelhelm's old dream, is not yet done.
Mathilde's has personal reasons to take her shot at it.
C. She's an excellent candidate, one of the best (if not the best) for the job. She could do a world of good.
D. I like reading about fighting Vampires and Necromancers, and transforming hellholes into places worth living.