Even though someone is ill for a long time Mari, you're never prepared when it happens. I don't know how to tell you to prepare for the service because I've only been to one since my mom passed, a friend I met in the hospital. The whole experience just brings back too many painful memories.
Maybe you could just go and pay your condolences and leave quietly. I always like to send something living, like a plant. Or maybe cook something and take it over to the house.
Whatever you decide to do, it's what's in your heart that counts