Well, you understand that different people have different systems or ways of doing things right?You do have your own money, right? So what business is it of hers how you choose to spend it? Does she have her own money? If so is it any of your business what she does with it?
I think my wife spends way too much money on clothes and shoes and cheap baubles and such, earrings and bracelets and that. But, it's her money.
Edit- what I mean is, no reason to question their relationship because yours isn't like that.