I'm not a guy, but I do work. A few things came to mind:
1. Do you share the chores around the home, sounds basic but I work FT too as well as my husband and while he is great there always seems jobs I do after he's finished for the day and relaxing. Does she feel she is doing more than her share. Now this maybe because she is particular in how a job gets done or does jobs that you may find unnecessary but this may be wearing her out, you need to talk about this.
2. The kids, do they demand more of her than you. Sometimes kids go through phases where they want one parent to feed them, bath them, read them a story and although the other is willing to help the kids demand more of one parents time. Or does she feel that she should be a stay at home mum and feels guilty?
3. Is it the job she is in rather than working per se. Is the job, hours, travelling, ppl she works with, getting her down Perhaps she could do something else rather than stop work altogether. Could she child mind or do something where she could stay at home?
4. Does she have any 'me' time. Maybe and afternoon or evening a week to do what she wants to be her own person for a few hours. That can make a big difference.
In summary you need to talk about it. You cannot have it all, if she does not want to work then you may have to downsize your lifestyle. You need to discuss together what you both really want financially and agree a solution together.
I get the feeling you feel bad that she has to work because your earnings are not enough. Many ppl today are in the same boat. So don't beat yourself up. You and your wife are a team and need to work together to provide for your family, either some of the 'things' in life have to go or you both have to work.
Praying that you will work it out together.