How to respond?

This is very hard all around. My best friend, my sister, has had labile diabetes for 28 years. Her sugars have been high for many years because her body is so sensitive to even a tiny amount of insulin, and it can crash low, in minutes. She's now developed severe numbness and horrific pain in her feet and legs, (neuropathy) because of the high sugar slowly clogging the nerves and killing them. She says the numbness is simply AWFUL.
She regularly says She believes she's going to die soon or next year. It makes me heartbroken, for her to be facing this MEAN disease or thinking at all about death.
It would be paralyzing in my life to lose her. She's my best friend and the most wonderful person you'd ever meet.🌹 How do I respond when she says every week, I'm going to die soon? I will typically be quiet not knowing how to comfort her, or tell her it's not true shes going to die soon and there's still breakthroughs in diabetes.
How else might you respond? 😕😔