Marriage in separation of goods

I really love my girlfriend, and I feel like it's mutual.
Marriage has never been a big deal to me but I know it is a big deal for her and her mother.

Her mother (who is half black and comes from Bahia) had a relationship half a century ago. Got pregnant, and the man she was with lied about his intentions of getting married. He refused to register the baby as his daughter and took off. She became a single mother.

20 years later she met a European guy, and it led to the birth of my current girlfriend. We have been together for 3 years at this point, and it works very well.

Since the beginning of our relationship, her mother is pushing me about marriage.
I get it from a religious viewpoint, and based on her past, but I was very skeptical about the financial aspect.
My (future) mother in law came from a poor family and all wealth she currently owns comes from her European husband, who died in an accident 25 years ago. At least that is what I have been told. My mother in law and my girlfriend have been receiving government benefits since the day he passed away. It literally bought them the apartment they reside in at the moment.

I believe that my girlfriend (who is white, which is surprising based on her mother) likes me for who I am, but her mother sees white people as superior and I can't exclude the possibility that she's after my money.

I remember that I was talking about enormous inheritance taxes in my country, and my future mother in law said something like "In that case this marriage is not happening". I said it to my girlfriend, but she claims that I misunderstood her. Mothers are special in Brazil so don't you dare to criticise my mother..

Either way, when I do get married it will be in complete separation of goods.

Is this something people fight about or is it common? I've never raised this topic to my girlfriend, because it is controversial