Tell her that you are opening a separate account, then do so and see how she feel/behave.

Nobody even care about if someone spends (I would say it an "investment" as better health is the huge wealth) $400 a year for fitness while a couple is spending over $5-600 a month for just for rent and about the same amount for food and other things per month. But, if she fights for small small things that bring in happiness in you, then the root of the problem may be the love, not the money itself. You got to talk to her heart to heart and figure out what she wants and let her know clearly what you want or you feel. Of course, behaving like a man is not the better solution and if there are problems in you  you also need to change yourself. But, if it is what you described here, then it may be stupidity to expect that she would be your love through out your life? You better prepare for the any worse situation now.