You persuade by listening. She is a smart woman, you guys objectively have plenty of money, so there is some emotional reason she can’t let go of that money. What is it? You need to hear and empathize and understand the “why” of it instead of insisting that ramping up the investments is logical — that just comes across as “this is so obviously the right thing that you must be a complete dumb-ass not to see it.” So basically, you think you are being helpful, she thinks you are calling her stupid — and you wonder why it ends up in a fight?
The only way to bridge the gap is for one of you to speak the other’s language. And since you are the one who wants to change her, that means you. Ask her what she is afraid of, and then listen — don’t fix, don’t jump in with “helpful” solutions, just listen, draw her out. Then you connect on an emotional level and ask questions to help her work her way through — e.g., you hate to see her operating with so much fear, because that seems like a lot of stress, and you don’t like seeing her worried and scared, especially when things are going well, so how can you help her feel more comfortable and at ease and confident?
And then over time you guys build the vision of your combined future that you’re working for, the things you want to do, places you want to go when you’re not tied to the job. If you guys can get past the impasse, and if she can feel heard, she may be able to put her guard down enough to acknowledge that you have a point about how nice life could be once you are FI, and that the way to do that is to save more now. It will probably take baby steps — maybe she starts with increasing her investments 1% a year, and when she doesn’t miss that, she pushes it up another 1%. Treat that as a huge win and be really supportive when she does that — it doesn’t seem like much to you, but it’s huge to her, so treat it accordingly.