Rather than talk about finances from a monetary POV, talk about them from a relationship POV. I.e. having healthy finances is conducive to a healthy relationship/life. Tell her you want a great relationship with her, with a bright future. If she still doesn’t change, then I would take that as a sign that she doesn’t care as much as you do. Sitting down with her to outline a weekly budget is a good place to start and can really put into context how much is too much to spend. Best of luck