I prefer eating fruit and vegetables (and I love grains and nuts of all kinds) but to manage my weight I find I have to eat a bunch of meat (more meat than I want). My brothers have found the same thing - as we've all got into our late 30s, we've had to switch to eating more meat (I eat mostly slow-cooker chicken) to keep from ballooning up in weight. But I also have to have carbs in the morning or else I under-perform at work. Anywho, your vague "natural"/"grandma-recognizable" stuff is completely useless for me: as a younger man I had no problem gaining weight on whole wheat bread (my mom ground the flour herself!) and home-grown potatos.
So what is it then? Maybe I ate too much? Well, you could say that for anything. Later in life, my mom lost a bunch of weight on some quack "HCG" diet (which is obvious nonsense, and yet it worked because it restricted calories). If you only ate things that being with the letter P on Mondays, you'd probably lose weight, at least for a while.. but it's hard to think of that as an effective meal-plan; it's effectively just "eat less".
"Don't eat too much" is an easy catchall, but is often completely unhelpful in terms of helping people make decisions that will make healthy living easier. And, for me, avoiding meats is advice that would make healthy living much harder. I've found a balance of stuff that's working for me (when other stuff didn't), and I'm mostly happy with my health/diet situation, but I've never seen some overarching theory that really fits my experience of health and nutrition. I imagine what you've presented is working for you, but it's not some universal home run - and I think a good chunk of it is baseless bollocks (or is correct by coincidence).
The very idea that there's a simple formula for how to do this is a big part of what's screwing people over; people glom onto some theory, and when they find it isn't working they blame themselves or give up. In the 80s, it was super simple: just eat less fat and you'll be less fat. That kind of sounds intuitive (man, people are eating a lot of fat these days, and fat is so calorie-dense!), and cutting fat worked for some people. Yet for many people, trying to cut fat was just going to make their life harder.
My sister-in-law is overweight and eats a bunch of nuts because it fits some Venn diagram of the 3 kinds of BS she's swallowed (and it would fit your plan too). But she's not losing weight. I think the nuts are making it harder. None of the people telling her things (and that's everyone; everyone is telling you something when you're an overweight female) are making things easier for her, and most of the sources she hears from in society pretty much actively shame her; they're saying "it's your fault for not eating more natural, for eating too much meat or gluten or dairy or whatever". Everyone has an idea, most of them backstopped by "well, if you're doing that stuff and still not losing weight, then you must be eating too much" and, again, the general notion "your lack of willpower is the core problem".
I don't think the answer IS simple. I think to help her, you'd need to sit down and look at all the things she eats and how much. You'd need to look at what she's doing, how she feels during the day, and what are the situations where she ends up really going off the rails and overeating. You'd need to try a few things, experiment through a few failures, and approach the problem from a few angles. "Her": the specifics of her body, her mind, and her life, would need to be part of the plan - such that if the plan fails, we don't say this external thing like "your willpower" failed, we say "we need a better plan".
Some people may just need a simple answer. For other people, I think "seeking the simple answer" is preventing them from building out the more complex answer they need.