Oh Christie I'm so sorry. This happened to a friend of mine in March. She'd had cancer for 5 years but kept it a secret from all but her immediate family. It was such a shock. I still miss her dreadfully. At least she didn't have children, but then again I know that if she hadn't had cancer she would have had children.
Please keep in touch with her family and offer them your support. They will appreciate it - not just now but weeks, months after her funeral. Don't feel you are intruding. You won't be.