Welcome aboard, Kimberley! When your window for online check-in opens (75 days prior to sailing for first time Disney Cruise Line guests), you will find the
Special services form in your information online.
The form is for guests to report any special needs, even though you may have already noted that on your reservation with your travel agent. This is the place to note that you'll need a special refrigerator and sharps container in your stateroom due to your daughter's diabetes.
The form is a PDF which you can download, complete and then either mail, email or fax the form to Disney Cruise Line using the information provided.
Disney is wonderful in assisting guests with all different types of needs, and I am sure you will find that they go to great lengths to ensure that your daughter has no problems with her medication accessibility in your room.
Please let me know if you have further questions before you set sail, Kimberley!