Tithing issues in Christian/non Christian relationship

I love my fiancé very much but I feel the church is taking advantage of her even at her donation rate of $400 monthly they will still bilk her for various other small donations. The issue is things are very expensive now days. We will soon need a house be having kids etc. She is beyond locked in to this manner practice in her faith. She has said she feels if she does not tithe the amount the bible said she is not following gods word and could go to hell. I don't understand what god requires 400 cash a month or you're not in good standing anymore. I have brought up the reality times are uncertain and we need to be wise with our funds and not frivolous. But the conversation always goes nowhere. How can I explain to her that basic requirements come first in a way that aligns with her faith? or is this very common and I need to re assess the situation?