Hi Justin! I just have a few thoughts on this. I’m sure you will get much more excellent advice from others on the forum.
As Catholics we believe that the Church has the authority to interpret scripture. The Church cannonized scripture, after all!
1 Timothy 3:15 says that the Church is the pillar and foundation of truth, NOT the Bible, which didn’t exist at that point! Which Church, your friend might ask? Well- hers wasn’t around back then… so it must mean THE CHURCH that Jesus founded, on the Rock of Peter. That would be the Catholic Church!
God in His wisdom gave us an authoritative Church to guide us in all truth. He knew that human nature, if left without such guideance, would twist things 1,000 different ways. Peter warned of such things in 2 Peter 3:16. And that is just what has happened with Protestants. There are over 30,000 different denominations, all with their own interpretation of scripture. Surely God could not have intended that! And if they believe that the Holy Spirit is all they need to interpret the Bible for themselves, then why has the Holy Spirit contradicted itself so many times, which is not possible for God to do? So in the end, their “interpretation” is really just their personal opinion.
Ultimately then, you can fall back on John Martinoni’s argument:
If a Protestant believes that all you need is the holy spirit for your own personal interpretation to be valid, then YOUR interpretation is JUST AS VALID as hers. Yours just happens to be not simply the product of your own fallible mind, but also that of over 2000 years of the best minds in history, AND of a Church that has been led and protected by the Holy Spirit for the same amount of time! The worst you can do is have a tie!
A word of caution: When 2 people care so very deeply about their faith, and they are very different (some baptists think the Catholic Church is the Anti-Christ, whore of Babylon, etc), it is hard to achieve true intimacy (sorry- I don’t know if a romance is your goal!) There is always a wall there- you’re not in FULL COMMUNION with each other. I feel that way about my sister, who, coincidentally, is a baptist. We agree not to discuss any finer points of theology, and keep our conversations steered toward other things. Sometimes that’s awkward! But when it DID go into Catholic things, she would always end her points with “It doesn’t say that in the Bible!” The idea of an authoritative Church doesn’t hold any water for her. I can’t personally imagine being married to someone that I am not 100% on the same page with. It has been done, of course, and successfully, too… and it has led to many conversions. But to me it would be very hard. Good Luck!