A Very Scenic Trap

Nancy Ann Gilders had married Harry Silvers after knowing him only eleven days. He was very wealthy, she was comfortable, but not rich. They spent four years in a very happy marriage. They traveled to many places. Then he was murdered with a very rare and hard-to-trace poison. He left a daughter and son and Nancy Ann. All three had apparently been cleared in the murder. All three became very personally wealthy at his death.
Nancy Ann had to get away. She made plans with the daughter to take a trip. Then it got scary. Was someone trying to get rid of all three heirs?