I agree.her mom needs to get informed and diabetic education.A diabetic can eat everything she wants As long as she gets insulin.
If she's not given insulin everytime she eats, she should only get food without carbohydrates:
Vegetables (except potatoes and corn)
Yes, that and also blindness and nerve damages.
Physical activity is also recomended for diabetics, but if the value is higher than 15 hard Physical activity can do more damage than good, but if she's lower than 15, running, swimming jumping (trampoline) etc. is very good for her.
Good luck, and please tell us what happens!