Eating whole natural healthy foods isn't necessarily cheap. We eat pretty healthy and I cook from scratch almost 100% of the time and I would say we definitely spend between 100-200 a week. This is for our total shopping costs, so that includes things like cleaning products, batteries, light bulbs, alcohol, nappies, etc. That's for a family of 3.
I find eating really good quality whole foods is expensive. I don't buy organic, but I do buy lots of fresh fruit and veg, which isn't expensive. But things like dried fruit, nuts, nut butters, other sources of healthy fats like avocados, coconut oil, olive oil aren't cheap. Quality meats aren't cheap either (we do eat meat, but maybe only a few days a week). I think it probably also depends massively on how much she is actually cooking herself at home. I always hear people say like, oh, I feed my family of 5 for 50 quid a week. Except what they mean is they feed them dinner. They are getting breakfast from Costa every day on the way to work. The kids are eating lunches at school and they are grabbing a meal deal 5 days a week from a shop for lunch. And then eating biscuits from the biscuit tin at the office for a snack. We might spend 400-700 a month on all food and household supplies, but that is like truly everything we spend on food. We eat breakfast at home every day. We pack snacks and lunch for work. We both take coffee in a flask to work in the mornings. We make lunches from scratch on the weekends rather than eating out, etc. We tend to invite friends over for lunches and dinners and drinks because we can't easily go out (no childcare) and that's expensive too, etc. So it ends up sounding like quite a lot. I think 300 a month for a family of two adults and at least one child doesn't sound like much at all, but it depends I guess what they are spending that on and how much money they are spending on other things (like meals out, snacks, household supplies, etc.).