She sounds like she's incredibly, incredibly bored. Does she work? Do you have kids, or family nearby? What's her social life like? How do you guys spend your time together?
What does she scream and cry about when you approach her about this? "This is how I have fun," or, "It's not that much money"? If it's something like the former, you have to figure out a gentle way to tell her that it's bizarre and sad (but also, I guess, pretty normal) to have fun spending money on useless things that probably never get their price stickers removed, and wouldn't she rather share fun experiences with you or other people? Or, at the very least, how enjoy the things she already has, instead of having them moulder away in the basement?
If it's the latter, I'd add up the full cost of what she spends. I'm sure that after a year or two, it'd be enough money to take a nice vacation, or--this may backfire--buy something you both REALLY want/need. Or that a full decade of not buying things advances your FI by however many years.