Look up "mansplaining". I'm not saying that's what you're doing, but reading up on this topic should make you aware of the ways that people (especially guys who are interacting with women) can unintentionally come across as condescending in different contexts. Empathy is incredibly important if you're going to try to adress this sensitive problem.

You absolutely don't want her to pass on her insecurities about learning to your daughter. (Remember the 1992 "Math class is tough!" talking Barbie?) You could try reading up on things like "math phobia"/"math anxiety" and research-based approaches to treating it. But in my mind, treating your wife with respect means that you need to follow her lead as much as possible and give her agency in directing any activities to address her ignorance.

First off, none of this really matters except to the extent that it affects your daughter. So I would frame any discussion entirely in terms of that. Also, you should try to avoid, under any circumstances, telling her -- or even in the slightest bit implying --that she's bad at math or ignorant or unintelligent or anything like that. This will be difficult, but as soon as she believes "my husband thinks I'm dumb," it's basically game over. You'll need to find some way to broach the subject, like "so I saw this article that says part of the reason there are so few girls in math and science is that they get think they aren't any good at math, maybe because they didn't quite grasp something early on or maybe got one bad grade on a quiz, and then they live the rest of their lives getting kind of anxious around math and thinking they're "just not a math person" -- what do you think about that?" It's easier to admit you're "just not a math person" than it is to admit you're stupid. If you're able to get her to admit she's "just not a math person", you could maybe then broach the subject of "what do you think we could do to make sure our daughter doesn't grow up thinking the same way?" Also talk about how research shows that non-"math people" can actually become "math people" at any age and that it's a matter of self-confidence and believing in one's ability to improve (Google "Carol Dweck" and see her talks on YouTube about fixed versus growth mindsets). Really, the goal should be to try to get your wife on board with self-improvement but for her to come up with the idea herself so that it's her project, not yours. And even if you already think you know which resources are best (e.g., Khan Academy), let her search for and choose resources herself.

Now, I realize math isn't the only issue, but if she can gain more intellectual self-confidence in this one area it might reawaken a sense of curiosity about the world and propel her to further efforts to develop her understanding of the world.

I realize that some of this advice is self-contradictory -- "respect her by putting her in control" vs. "make her believe it's her idea". I don't know what to tell you. It's not an easy issue to address.