Wife's money or marriage money?

Being married for almost fifteen years and my wife has her parents in other country. Her parents live with my wife three other siblings (two sisters and one brother) all of them work full time and are over 30s already. My wife’s parents are in the 60s and they don’t really work. The problem is my wife keeps helping them economically every month and doesn’t want stop doing it (I know it is over $100 every month and she keeps saying that it is her money and can do anything she wants with it [after she pays some bills in our home]). I am tired being arguing about it every month because we have kids and I want safe money for things we need here. However, I feel that they too tie each other and live as never will go out of that house (they are paying the house). I don’t know what to do because I don’t want to lose my marriage but she gets mad with me every time I spoke about it. Thank you for your feedbacks.