Hi helenbran,
Very briefly, a healthy non-diabetic blood sugar will usually be in a pretty tight range around 4 or 5mmol/l. After eating it can rise as high as 8mmol/l, but will fall back to its normal range within a couple of hours. Your mum's figures are a bit higher than that, but if she reduced the amount of sugars and starches in her diet she will find immediate improvement.
The best reference book for these sorts of things is Dr Bernstein's Diabetes Solution. Dr Charles Clark's 'The Diabetes Revolution' is another good source of information and currently on the shelves in the big bookshops.
All the best,
fergus