Hi Chocnuts and welcome to the forum.
The policy that Sam got wasn't straightforward life assurance, if that's what you are after. Sam's policy is what is usually called a limited term mortgage protection policy. Her policy lasts only 10 years and each year the amount that they would pay out in the event of your death reduces (that's where the "decreasing" comes in).
If you are looking for a "whole life" policy - one where you pay a regular premium every month until you die - then you will need to talk to one of the specialist diabetes insurers because the big insurers (like AXA, Norwich, Prudential, L&G, etc) usually don't want to know when it comes to diabetes, or they will quote you an astronomically high premium in the hope you will go somewhere else!