I'm Type 2 and a confirmed low-carber, which is the diet that the nurse seems to have recommended for your mother - "no starchy carbs". However, I am still producing my own insulin.
Basically, every gram of carbohydrate that you eat is turned into glucose in your blood; insulin helps use the glucose properly, as energy for muscles, and storing the excess as fat. Without the insulin your body can't use the glucose for energy, so it burns fat and muscle instead, causing weight loss. Your mother now needs artificial glucose to cover her carbs, as she's not making her own. Fewer carbs in the diet = less articial insulin, but if your mother likes to eat carbs and won't eat much else, you may need to use more insulin for her.
Sorry if you know all that already!
You do not say how old your mother is, but you do say that it is hard to get her to eat enough. If you are responsible for getting her meals, you should have been given information on how to balance carbs with insulin, so that your mother eats enough carbohydrate to balance the insulin she is taking. There is a course you can go on for this - called DAFNE, I think, but I could be wrong!
I think she
should still be eating carbohydrate, but perhaps less than previously, and going to low GI carbs - wholemeal instead of white bread, always new potatoes, brown rice and brown pasta rather than the usual white versions. The important thing is to keep her eating. In your place I think I'd go back to the nurse and ask to talk to her again, as to how you're going to get your mother to eat enough.
Why not ask your question again on the Type 1 forum? I know your mum is now an insulin-dependent Type 2, but if you can't contact another Type 2, the Type 1s are the insulin experts.
Good luck!
Viv 8)