I don’t think you CAN make her nap because you’re right - she doesn’t need it because she IS getting sleep. (YOU’RE the one who isn’t getting the sleep and needs the nap because you’re doing what
I think she should be doing!)
When I have a newborn, I am up late at night with them because I know my DH needs to work the next day. Then I’m up early with the baby so DH can continue to sleep. So, on the nights before DH works, I’m in charge. And that makes me tired, and wanting to nap that day. Which is perfectly fine and normal! So I nap!
If you can’t get her to take over the 4am shifts for a week while you recharge your batteries, then maybe you should come right home and nap so you’re ready to go that night.
PS - I don’t think she’s a bad wife. I just think that she’s doing the same thing I would do - if my hubby did what you’re doing and never told me how exhausted he was or complained to me about it, I’d assume he was 100% fine with the arrangement and I wouldn’t try to change anything about it. After all, I like sleep too! But as soon as he told me otherwise, then yeah, I would take over so he could function at his job.
Sorry if this sounds like I’m rambling. I’m needing a nap myself about now.