I forgot to mention one very crucial thing: testing for ketones. If your mom isn't doing this already, she needs to pick up some Keto-stix or Keto-diastix from the pharmacy. They're test strips that you dip in the kitty's urine which indicate whether ketones are present. Trust me, you don't want ketones. They can quickly develop into a life-threatening condition called ketoacidosis, and treatment is very expensive (24hr emergency care for several days). Unregulated diabetics are more prone to this. Here is more info:
http://petdiabetes.wikia.com/wiki/Ketoacidosis
And along with the felinediabetes.com website that MBIE mentioned, here is another one that is a wealth of very up-to-date info:
http://petdiabetes.wikia.com/wiki/Main_Page