I was thinking on the Lannister/Crown retaliation of Sansa/Ramsay/LF and this is what I came up with. (One term I will abbreviate Men of Fighting Age, MOFA)
1) Which kingdoms/areas would invade the north over Sansa? Reigniting war and debt.
Vale - No
Iron Isles - No
Riverlands - No
Westerlands - Absolutely
Stormlands - Probably/maybe (some may still see Tommen as a Baratheon)
Dorne - hell no
Dragonstone - no
Reach - Since Margery is Queen, perhaps they march, but it would be very half-hearted. (Remember they conspired with LF to kill Joffrey). If they march they may pivot to kill off the Lannisters.
What is the state of the Lannister war machine? Broke. No! In debt. I think its reasonable to say they have less than half their MOFA. (Tywin split his armies into two Jaime with one, and he with the other, likely another third played defense in casterlyrock, KL, certain keeps). The battle where Jaime was captured prolly knocked out 1/3, then there was a dance for months, but Robb was pillaging the westerlands. "they are winning" tywin. iirc the lannisters were forced to purchase sellswords. It may be plausible that of Westerland men, they may be down around 1/3 from the start of the story. But some would inevitably have to play defense again. The lannisters ability to campaign, to pro-ject, is gone imo.
Stormlands how many died at the Blackwater? After Renly, some went with Stannis others with Loras. But they seem leaderless. Even if the banners were called, who would they be loyal to? The answer is Tommen alone. They dgaf about Kevan or Cercei. So Tommen would have to lead the charge for revenge. Considering he benefits from his brothers death (Margery's twt and the crown) why does he seek revenge. Plus Margery would have to convince him, and she has the ability to dissuade him.
Since the North is likely at ~40% MOFA they are still a threat. And even if the other six kingdoms magically aligned, most Lords arent dumb enough to march on the north on the eve of Winter.
So I contend, there isnt a single country that could/would attempt to bring Sansa to justice, which makes the plausible alliance with Stannis more entertaining. She is seen as someone who killed one of his usurpers, that must endear her to him on some level, plus she has the right name. The only problem is, is she were given warden of the north, she is expected to marry. There arent too many lords left to align her with. Marrying her to LF or Robyn doesnt help LF, he considers her an asset already.
Dorne has female heirs, they arent gonna introduce the dude who crispies in Mereen. I dont think Loras is available, nor to I think they would openly rebel against the crown while they have a queenscrown on Marg. Iron Isles, maybe one of Balons brothers. Sansa is without strategic bachelors.
BUT! The world is different if Jon is a Stark.