Check the instructions in the packs, you will find it is often OK up to 20C
Pack it in a plastic bag as with liquids for security, and put that in another waterproof bag, crew will give her ice to keep it cool.But do NOT allow ice to touch the vials directly (freezing it is worse than it getting a bit warm)(I also put spare needles etc. in same bag)
Check your local chemist some sell purpose made cool bags for insulin etc.
do not put anything in checked in luggage everything in hand luggage
Do not order Diabetic meals - they are not suitable for insulin dependents, carry some biscuits in hand luggage as well.
Flown to the states twice, no problems