Mine struggles mightily with this. Even the idea of it and if she does it the "momma guilt" just consumes her. On the rare times where she has "free time" I always encourage her to take time for herself. Yet, most if not all of our marriage she's struggled with it. Guilt sets in if she takes any time for herself. I've tried everything I can think of, practically to the point of begging her to do so and she doesn't or won't do it. I don't get it. Yep I get men and women are built differently in this regard. There's been occasions where not doing it has bubbled over to where I basically tell her to go anywhere but near the kids so she can have time to decompress. This makes her angry at me. She's not mean to them, and she's a great Mom, but you know how it is when you go, go, go, go, go, and let the lava rise to the top before the pressure finally makes it burst. That happens on occasion. Then if I even dare point out that if she took time for herself this would probably decrease the chances of a blow up....that just makes her madder, so it's like spitting into the wind.
Wish I knew the magic pill to help her understand self care is actually one of the most important things she can do. She's amazing in just about every way, and it's a massive challenge for her to do it.
I outkicked my coverage with her. She's amazing in all the ways I'm not, but on this one thing it's been near impossible for her to do it. Wish I knew the magic wand, but there isn't. Maybe it'll just take time for her to slowly come to the realization.