Fortunately, the heroine was, in the last story, already talking with men in the army about this, and men familiar with deploying sorcery with their swords. Her role is to implement the magic that helps sneak, and do the sabotage, with enough guards to guard her back while she does it. Guards who know that military stuff.
But "Free Passage" it ain't -- I like a battle where the heroine's actions are "run behind the swordsmen and crouch to minimize the danger."
On the bright side, none of the earlier stories described the necromancer's lair in any detail, or indeed anything except the fact of its existence. And she also has some scrying magic, which will help, unless they have better. I have to decide.
Hmm. . . OTOH, the necromancer has been able to use other magic, they suspect he's traded for it, but perhaps I need intelligence that it was quid pro quo, so they only have to worry about his necromancy and whether he's used something in his lair that he wouldn't use out of it.