Yes in deed the whole relationship is relevant. You are wrong to try to solve this one piece at a time. But, having said that, regardless of what happens in the relationship she needs to get a handle on budgeting. If you stay together and heal all the rifts, she will need to have respect for you , and you will need to trust her. Money is part of that. If you part and co-parent, she needs to be able to sanely run her own household without running to you or a judge for more money every 3 months. In fact unless her Dad is willing to fund her long term and steadily, she has to know how to budget. Her lack of interest in the subject can only be cured by deprivation. She will have to lose something.
Deprivation is a word that has been on my mind. I know that I need to make some hard decisions that she will have to agree with. Just this past week, she wanted me to agree to turn a trip to Alaska into a two week family vacation. That is all well and good if we have the money. A few months ago, when the trip was proposed, we agreed that if she would have the money for airfare by January (now), then I would agree to the trip. She doesn't have a penny saved for the airfare. So I said no to the trip. She can go with our daughter, who is a bridesmaid, but I am staying home. We simply do not have money for the trip expenses, much less the plane tickets. I backed it up by going over the budget for my pay check with her again, showing her how my pay barely covers the bills. Best case scenario is that I would save $400 for the trip.
Her response was to go to her sisters, who said that they would pay for my plane ticket. I said no to my wife, who then insisted that I email her sister to explain why. I called her sister, thanked her for the offer, and told her that my wife and I need to learn how to work together to live on what we make, that this was an opportunity to make the hard decision that may send the message that I am serious about working together to live on a budget.
I put together a day to day menu for our meals this week, talked about it with my wife, and did the grocery shopping on Sunday night. Last night's dinner was a hit (sausage lasagna), only one small helping left. But after dinner, she sent our son out with a $20 bill to get ice cream, didn't ask me about it. When I asked her why she did that, her reply was that it was her money and for that reason it shouldn't matter. Tonight, they both decided that they didn't like what was on the menu (turkey chili with cornbread), cooked the frozen pizza that was for Thursday and ate it all before I got home from work. Seems like a small thing, but it was incredibly selfish and an insult to me.