How much for a weeks food?

I've been keeping a spreadsheet detailing my weekly food shopping since the end of February. I started off eating from stores and so on, but that was more than 3 months ago and most of the stores have now been used.

However - I'm still averaging £16.68 a week on food (that's all food - the weekly shop, any top-up shops that I do, the odd coffee out, a takeaway once a month and very occasional lunch with friends). This week's total was just £12.55.

I wrote a blog about how I do it - https://middleagedfreeandsingle.com/2019/05/16/husbanding-my-resources-oh-the-irony/.
As to meat - I'm evangelical about rubber chicken, so that accounts for 3 or 4 main meals a week and 3 lunches. For my other main meals, I always have fish once a week, red meat once a week, and a meat-free meal once a week, which I think is a sensible, sustainable, healthy balance.
I wish your friend well - there's a lot to think about and it sounds like she's tackling it head-on.