I can totally relate because I grew up in church with a Christian family. I don't believe in it anymore, but I still go to church on Sundays for the sake of my family. I'm currently in church as I write this lol. My point is that the whole 10% thing is not to be taken lightly. The pastor at my church constantly preaches about it and would even show videos dedicated to talking about finances and how to handle your money and how much to donate. It's such a big thing that my aunt will tell my cousin every time something bad happens to her that that thing happened because she didn't donate some of her money to the church. For example, my cousin dropped her phone recently and cracked the screen, then her mom said that happened because she doesn't donate her money. Thats pretty fucked up if you ask me. Point is, there's a reason your gf feels so obligated to donate 10% of her income to the church. It is commanded in the Bible, but honestly the church needs the donation that way the pastor gets paid, the church can pay for its bills and so on. Even if she's left with around 300 after donating, that "girl stuff" really does add up. If you're talking makeup then yeah you can buy 2 things at ulta/sephora for like 50 bucks. I'm not saying this is what your gf gets, just stating how easily the money can go if you're not careful. Speaking from my own experience lol. Now I'm still living at home with my parents, so I can get away with this every now and then, but unfortunately your gf still needs to work on managing her money better. She needs to prioritize and come up with a budget that will benefit you both. Maybe she can donate less to the church because even something is better than nothing. Either way, just talk about this with her and hopefully you can come to an agreement :)