If Edwin can't do it (he's on the wrong side of the map, too), Raquel's the only option left; Seyena can use staves, but has a range of 2. OK, I am really glad no one's moved yet; that may let us pull this off. Seyena has 8 move, Raquel has 6. With that, Raquel can move to (11,6), right next to Ami, by moving over everyone else. There, she can trade her Vulnerary to Gregor (which gives everyone still standing healing capabilities) and take Ami's Rescue stave, then electrocute or heal someone. Meanwhile, Seyena moves 8 tiles to (19,13) - this puts her four tiles away from rescuing Matilda and keeps her out of range of the twin Frannies and their eponymous axes. Next turn, Seyena moves four south, picks up Matilda, and moves four north, right back to where she started. Raquel moves back to (16,7), and with a range of 11 on the Rescue staff, she can just barely reach Seyena, hauling both of them right out from under the pillagers' noses. Of course, that assumes that demolished houses still block movement - I want to make absolutely sure, but that is correct, isn't it?
The biggest threat to this is someone KO'ing either Seyena or Raquel, which means we absolutely must sleep Wyvern Knight C, and almost probably-certainly zap Paladin B. We'll still be running a bit of a risk, but if Raquel gets KO'd, the most that happens is that Seyena comes back without Matilda. If Seyena gets KO'd...well, let's not dwell on that. As such, implementing the plan will rely on if Edwin aims for and hits Wyvern Knight B successfully.
As for why Ami can't do it, she can't reach due to the snow (cutting her move to 3) and 10 range. She can't move through Alex, Valor, and Riven because she'd have to stop at Riven. Moving one north to detour (assuming we eliminate Paladin B to get him out of the way) then back south puts her 4 tiles out of range of Matilda. Even with the higher move and range thanks to Levitation, Raquel is still two tiles short of reaching Matilda on her own - we need someone to push Matilda that tiniest bit closer. Regarding Alex and Valor, it is a major threat. There is, however, one other potential boon. That tile I specified for Seyena, if the pillagers can't move across the destroyed building, isn't just out of range - if they try to reach Seyena through the snow, they can't reach her for three enemy phases, and she should be gone, whether by Rescue stave or by her own pegasus, after two. I'm still worried of all those other enemies right on our doorstep, though; we can't take down all of the wyverns and the Paladin in one turn, and they just keep pouring through. Still, we have five people who can heal right now, at least a little bit, and with the modified Vulnerary trade in this post, we'll have six (since Charlotte gets to keep hers). If Charlotte goes down next to Alex due to enemy attack, it will put a crimp on healing him, but that's also what the Rescue staff can do - pull Alex out of the way so someone else can revive him, then let Gregor (since he's very unlikely to be KO'd) slip into where Alex used to be to heal Valor.