Securityregulations do allow a person to take medication in some kind of small portable cooler on board of an aircraft. A lot of airlines either don't have refrigerator on board or allow usage of them, even for medication. So the simplest thing to do is to bring something yourself, like a coolingbag. As this being for medical reasons, most airlines treat it as free luggage, it wont count toward the max. weight of luggage and carry on. To make sure what the specific possibilities and rules are of the airline you are flying with, she would best contact the airline. Most of them have a special department for flying with a disability or disease, which can be of assistance. They can explain their policy and if needed arrange the things they need to arrange for your trip to be as relaxed as possible.
Also a coolingbag of her own would be a great extra insurance, just in case she arrives at her hotel finding the requested fridge not working (and not being replaced/fixed within no time) etc.
