The number of carbs per meal depends on her own carb tolerance - we are all different. Personally I eat under 30g a day. Others eat more, others eat less. Cutting carbs means losing calories for energy, so she needs to make up those calories by increasing the amount of fat she eats. She can do this by ditching any low fat products and swapping for the real thing - butter as an example, avocados, certain nuts, cheese, unsweetened full fat yogurts, oily fish etc.
She needs to test before she eats then 2 hours after first bite. To test out new foods it is also a good plan to test at 90 minutes after first bite, and maybe also at an hour. By 2 hours she should have recovered from any spike. If the rise from before to 2 hours after is more than 2mmol/l (Preferably under 1.5mmol/l) there were too many carbs in that meal, so next time it needs tweaking - avoiding some or seriously cutting down the portion size. It is best to keep a food diary and record her levels alongside, then after a period patterns will emerge from which she can learn.
The worst culprits are bread, potatoes, rice, pasta and cereals, plus anything made with flour. We also need to be careful with fruit and milk. Persuade her to use her meter to learn which foods she personally can or can't tolerate.