My mother’s side of the family is incredibly Catholic, with a particular devotion towards Mary. My father’s side are a mix of Protestants, (he was Presbetayrin - sorry, spelling!) SDA and a few Mormons. So when my dad started dating my mum almost 40 years ago, well, you can imagine! My dad converted right before they married, and he was a devote Catholic and fully involved in the Church, until he decided to committ adultery 15 years ago.
My uncle married a Protestant woman and while there was a lot of pressure on her from his mother (the very Catholic Matriarch) to convert, she didn’t right away, it was actually 8 years into their marriage when she finally converted. I don’t know if they were practising NFP, or what her opinions on the matter were, but they ahve four kids, one autistic. And they’re still going strong.
It seems to me its dependant on the Catholic and the non-Catholic as to whether the relationship will work. I"ve seen mixed marriages crash and burn, while others have flourished, some without conversion, and others with - though, I have to say, once the non-Catholic spouse has come to full understanding and research of teh faith they converted. The other thing I’ve noticed, is that sometimes, a lot of the stress and misunderstandings are fuelled by outside sources, like an inlaw pushing for a conversion towards a certain faith, or friends putting their two cents in. It’s fine when its online, we’re all basically strangers, you can ignore us, but you’ll have everyone and everyone in your life who knows about this poking their sticky beaks in - for the most part.
I think that’s what’s important, as others have mentioned, take her along to an RICA class, if you and her are really keen on a life together, its important to know about each other’s faiths. Learn about hers, so she will have more desire to learn about your’s.
But I would say to do this research BEFORE you get married, so you both know what you’re going into. She needs to understand the Church’s teaching on life and contraception in particular, as ALL the real life Protestants I’ve met are pro-contraception, albeit, I’ve met a few online who have the same opinion as Catholics.