In the interests of coming up with something better than just 'attack', I'm gonna take a take a go at coming up with tactics.
We do have advantages here. We got what we wanted out of going to the mines: we rallied the mutants, put Etelka in our crosshairs, and hold a chokepoint. On top of that, and more importantly than it seems, we won that battle. Winning means that we hold the initiative and that the enemy's vanguard is spent.
There are three threats right now: Etelka, her champions, and the threat to the mine's supports. That last one is bullshit, but first let's talk about how to deal with the three bad guys.
Etelka is simple: spend Resilience and shoot her in the head with a Critical. It'll either kill her, disable her, or hurt her bad enough she runs away (might also run away just from blackpowder panic). All options are acceptable.
The champions are trickier, because their size and metal armour makes them brutal in a straight up fight, and their armour blocks insta-crits. Thankfully, we have three solid advantages: we have numbers, we have spears, and the beastmen's size inhibits their ability to fight in the mines (their horns are scraping the roof).
We can have the militia move to an area of the mines that has even less headroom and fight there. Markus and a few militia can stay on the front and focus strictly on the defence (+20 bonus to defending) while the rest of the militia surrounds the beastmen and stabs them from outside of their reach.
Now, as for the mine supports. Telepathy is very rare in Warhammer Fantasy, so the beastmen won't start burning down the supports until they actually receive orders for it. If we take down Etelka and the champions, they won't know to burn them down until enough time passes and it's clear Etelka is dead. By the time that happens, the militia can move to one of the mine exits and hold that position until dawn, when we can expect reinforcements; it'll be just as much a chokepoint as here and it'll stop them from burning down the supports. If Etelka survives our shot, it'll be a good amount of time before she can return to the surface and have her orders relayed to the beastmen at each of the mine exits.
However, that's the worst case scenario - the situation may be even better than that. See, our people need good light to see, but even they don't have fire, so why would the beastmen, who have good night vision and needed stealth to launch their attack? Etelka might straight up be bluffing. And on top of that, it's important to remember that this was once a dwarf mine, meaning it's sturdily constructed and unlikely to collapse that easily.
[X] Plan: Mine Holdout
-[X] Spend 1 Resilience to roll a 10 for shooting Etelka in the head
-[X] Lure the champions where there's lower headroom, surround them, and have the front rank on the defensive while the rest stab them
-[X] Move to one of the mine exits and hold the chokepoint until relief arrives.