3rd shift effect on family, health, marriage?

My wife is considering a job at a hospital working 3rd shift. She'd be working 9 pm - 7am 4shifts per week. She currently works 1st shift (as do I). We have 2 kids in grade school. She would take a pay cut (about $20k per year) to take this job but feels this is her 'dream job' as it's what she wants to do. She also feels this will give her more time with the kids after school. I work 1st shift with a long commute (out before 7 am, home after 9 pm most days) and am often not home until late so I would rarely see her at all during the week. I'm concerned about the effects on her health as well as she suffers from depression and seasonal affective disorder already. My other concern is our relationship. We've had a Very difficult marriage and have been to counseling previously due to a lack of time together. I'm afraid this job will effectively end our marriage and further exasperate her depression and health issues. I also don't believe she will have more time with the kids as she will need more sleep with the shift change (especially if depressed). I want to be supportive of her, she really wants this job as it's in a prestigious hospital and she doesn't want to work in long term care anymore. She has a doctor who wants her ton run a private practice he is acquiring, I have tried to convince her to wait for this as she could get credentialed and see patients at this hospital in this role. I'm at a loss with what to do. If you had experience with these types of situations and have advice it'd be much appreciated. Also wondering if I'm making a big deal out of nothing?