When you take out the stuff that's likely to last more than a week (she buys a bunch of herbs and spices, flour, jam & other things in her initial £35), it works out to not much more than £1 per person per day, which for 3 meals, including a fair bit of meat & fish, is good going.
Home cooked food is one area where I make very little attempt to be frugal - it's just not big enough an expense to be worth me worrying about, but for students, or hose on benefits (or whose benefits were stopped, like the author), this is a great resource. I've made a few of the recipes since Kitsune posted the link and they've all been pretty nice.
At the time of the original post, I could knock a fair bit off her budget, because (in November) there are thousands of apples going free round here; most people don't even bother to pick them. Similarly, I could've had tomatoes, spinach and onions from the garden.