Well I doubt everything she buys is laden with animal fats, but here are some rough guides to prices and what you could buy. Ask her to make sure she stocks up on canned food like italian tomatoes, chickpeas (you can make your own hummus and its great in curries and soups), lentils, kidney beans etc. I doubt she'll shout at you, it's cheap and great for the whole family, and just suggest it as a non vegan thing.
Cauldron Organic Tofu £1.49 (£5.96 per KG)
Kikkoman Soy Sauce 150ml £1.29
Vegan Bouillon powder £2.25 (or any real vegetarian stock, check to make sure its vegan friendly as some add in milk solids)
Alpro Soya Milk 1L £1.29
Setian quickmix £3.99 (its a wheat gluten thing, i've never tried it but several people I know like it so..)
Other foods:
Japanese mirin (great for marinating tofu, along with soy sauce)
Organic soba noodles
TVP or wheat gluten (such as quickmix) (runs around £3-4, cheaper at an asian mart)
Sweet potato and sweet carrot
Vegan-friendly bread (last time I was at waitrose it cost about £2 for a brown loaf)
Sundried tomatoes
Theres a great brand over here in New Zealand called Sanitarium and they make this absolutely delicious product called Tender Pieces, which is basically wheat gluten in gravy.
I'm going to stop now because I haven't lived in the UK for a year and its taking me ages to research what is available, but i'd recommend going to
http://veganfamily.co.uk . Its a website run by this scottish family, its really interesting, incredibly informative and just generally a good read, plus check out the links section too, theres lots of blogs and recipe sites, and some of them have links to what they have in their fridges.
If that fails, just show the videos on
http://chooseveg.com to your mother. That might shock her into buying less meat products =)