Those numbers yo-yoing like that would worry me, they are seriously high. Unfortunately diabetes in the very elderly seems to be just accepted by the medical profession, and very little notice taken of fluctuations in levels. If she is getting readings like that, they HAVE to take notice as it could be causing damage, and as she is getting forgetful, that is another worry. If mum is agreeable, I wouldn't even wait for the DN (what on earth do they mean, don't adjust the insulin? Surely they can't be saying those levels are acceptable?) but I would contact the GP, and explain your concerns about her extremes of levels, and also her confusion/forgetfulness. Urinary infections are extremely common in the elderly, and can cause awful dementia-like symptoms, so it makes sense for her levels to be within a reasonable limit, not off the scale like this!
Please ask mum's permission to contact them, then give them hell. They are risking her health and wellbeing in acting in such a negligent way.
Good luck.