Sister flips out over intended name for unborn nephew

DEAR ABBY: I am pregnant with the first-born grandson on both sides. My husband and I plan to use my husband’s middle name for our son’s first name and my father’s middle name for his middle name. My father is “the III” but has no sons, so we thought this would be a way to honor him and represent my side of the family. My sister is the first person we shared our son’s name with. The following day, she called me to express her displeasure, because she always planned to use our father’s middle name as a first name for a son. I knew this, but I didn’t think using it as a middle name would be an issue. Additionally, she’s younger than I am, unmarried and childless.