PMS isn't a punchline — here's the actual playbook
PMS gets treated like a joke, and that's precisely why it goes wrong. The eye-roll is the problem. The week before her period is real, her body is doing real work, and if you treat it like a bit, you'll get treated like part of the problem.
So here's the actual playbook. Not "survive her." Not "walk on eggshells." Just a handful of moves that make the week easier for both of you.

Lower the stakes, keep the effort
This is not the week to reopen an old argument or drop a big decision on her. Which flat, which job, whose family at Christmas. Park it. Pick a calmer week. It will still be there, and it will go better.
Meanwhile, handle the small stuff without making it a thing. If dinner is sorted before she has even thought about it, that's one less decision on a day when decisions feel heavy. Concrete beats sympathetic every time. "I've got dinner" does more than "let me know if you need anything," because "let me know" quietly hands the job back to her.
Answer the mood, not the transcript
Some evenings the snappy comment isn't really about the thing she snapped about. I'm not saying ignore her. I'm saying don't litigate the exact wording of a sentence she said on no sleep and a stomach cramp. Let it go. It usually wasn't the point anyway.
And when you're not sure what she needs, ask a smaller question. Not "what's wrong," which can land like an accusation. Try "want me to sort dinner, or do you fancy getting out of the house?" You're offering, not interrogating.

The point isn't to fix her mood. You can't, and trying makes it worse. The point is to not add to the load, and to be the calm thing in the room instead of one more thing to deal with.
You're not managing a crisis. You're just not being one more problem to solve.
Do this for a couple of months and something shifts. The week stops being a landmine you tiptoe across and starts being a week you both know how to handle. That's the whole win, and it's a bigger one than it sounds.