The bottom line my friend is that real estate investing has made the most wealthy people, no other field. She needs to understand how much better her and your and your children's lives will be if you can sacrifice a tiny bit now and put together some serious foresight about the future. If you can invest in a multi at your age to start your life, you'll be so happy.
I convinced my then GF to let me buy a multi family that we could live in when we started and then hold as a rental when we moved out. She was completely disinterested in real estate and still is, but I had the knowledge and had to just believe in my plan and showed her the proof that it worked. She doesn't care about money like I do (but really, she does, as do most people who say that, when they see what it does to your life eventually) but the convincing angle has always been "look, this is how we are going to make the most money over our combined lifetime so that by the time normal people retire we'll have been set up for decades, able to travel, send our kids to any school, etc." and she trusted me, I just didn't stop until she did. It was a great decision and I'm now fully entrenched in real estate. You don't have to be a know-it-all or try to control the relationship, but if you have this knowledge at such a young age which sounds like you do, you need to do what you know is going to be right for your future family, and that's investing in real estate. You should try to appeal to the family idea -- your future family will be so set up if you do it right, and if you wait you're only losing money via opportunity cost by the day. My ultimate advice D'Andre, you have to keep pressing her and make it work, and then keep scaling from there. You and her will never, ever regret it. Just let her be part of it, decorate the first house hack to her liking, whatever she wants. You are about the numbers because you know it works, she has to just be brought on board. It's very difficult to have great foresight at 21 but it sounds like you do. Do whatever it takes to get her on board. Good luck man.