Why was Annemarie surprised by Uncle Henrik's announcement that there was to be a funeral?

Annemarie was surprised because she hadn't heard about a death in the family. She also knew that they hadn't received a phone call informing them of a death, but most of all, Annemarie knew nothing about a relative named Aunt Birte.

And—most puzzling of all—she had never heard the name before. Great-aunt Birte. Surely she would have known if she had a relative by that name.