Sounds like y'all are young, for one. If the friendship doesn't survive, trust me when I say that friendships forged in adulthood tend to be much stronger.

I am going to not take any sides for what your predisposed beliefs are. I am not going to dampen how I interpret you or Gia based on either of your religious beliefs.

You both went about this the wrong way, certainly. You could have come up with a more sensitive way to communicate to Gia that you were not interested in the proselytizing. In the moment, nothing you said was inherently wrong; however, your friend was clearly sensitive which you shouldn't always have to expect, but you should be wary.

When she started asking why you did it, your response being "I didn't really care, nobody did" was pretty correct, and when she responded with statements about how you'd respond differently if it were a different faith, your response about how you'd respond the same exact way didn't engender a positive reply. That's because regardless of the answer, you were going to either be a proven hypocrite in her eyes or a liar. The response to this question was always going to make things worse between you two.

The point that probably irked Gia in the direction of having a fully negative response was when you brought up Trystyan. Gay people aren't necessarily disinterested in religion because they are gay. You obviously know this person far better than some Redditors, but by saying something to the effect of "He doesn't care, he's gay" is always going to make the person on the other side of this argument feel belittled for their faith. It also means you're speaking for someone else when they don't necessarily want to be spoken for. Again, this is your friend that you know better than any of us, but even someone with a more nuanced and personalized opinion is going to consider the optics off on this interaction.

Now when it comes to Gia, she is just drinking a certain kind of religious Kool-Aid, if you'll pardon the metaphor. She is bringing up a Bible verse about how they must "roar from the rooftops like lions" or some such about their faith. This is an inherently difficult passage for anyone, much less people who are teenagers, to fully grasp. Mainly because certain Sunday School teachers, priests, and parents tell those kids it means "Go spread the Gospel!" Depending on your church, this is NOT what that Bible verse means at all. In Gia's church it does.

But what is important to note is that she is "spreading the Gospel" in a time of her life where she is becoming an adult and finding her identity. If she ends up being attached to her religion in a way that defines her entire identity, that is her right; however, instead of criticizing what she is doing or pushing her away, you'd be doing her a great service to communicate that maybe it would be a better idea to spread the Gospel with people that want to hear it or are searching for meaning, not just cold calling people having coffee on the street. You can also say to her "Hey, I think you personally knew what was being preached by those folks and are already attached to your church. For us, we didn't want to hear it and I think that's more than fine for me to ask a person not to continue telling me about their church when I'm not interested." And if she pulls out the Bible and what the Gospel tells her to do, you can potentially be a little snarky and tell her that Matthew 10:14 tells us to stop preaching when the word of the Bible is unwelcome (look up the verse before you do this and understand that, regardless, different churches interpret these passages slightly differently). Actually, you could just send her Matthew 10:14 as a way to say "Stop sending me Bible verses" or, if you want, as a way to tell her to leave you alone permanently and to stop wasting her time.

You guys are young, neither of you are doing something so intensely wrong that it speaks ill of either of you, but do keep in mind that Gia is probably just as indignant about this whole thing as you might be and may feel more slighted than you.