Princess Diana wore the "Spencer tiara" on her wedding day, July 29, 1981, instead of selecting one of the many tiaras owned by Queen Elizabeth II because the Spencer tiara has historical significance and holds special sentimental value for her. The Spencer tiara is a family heirloom that had been passed down through generations in the Spencer family, Diana's maternal family line.
The Spencer tiara, also known as the "Spencer Family Tiara," is an elegant piece of jewelry that features a beautiful design with scrolling motifs and diamond accents. It had previously been worn by Diana's sisters, Lady Sarah Spencer and Lady Jane Spencer, at their respective weddings before Diana wore it on her wedding day.
As for whether the Spencer tiara has been worn publicly since Diana's wedding, it has been seen on a few occasions after her death. For example, Lady Kitty Spencer, Diana's niece and daughter of Diana's brother Charles Spencer, wore the Spencer tiara at her wedding in July 2021. Lady Kitty Spencer's wedding marked a public appearance of the tiara since Diana's wedding in 1981.
Regarding the inheritance of the Spencer tiara, it traditionally passes within the Spencer family. After Diana's passing, the tiara likely remained in the possession of the Spencer family, and it is expected that it will continue to be passed down to future generations within the family. However, specific details about the inheritance of the tiara and who will be the next recipient have not been publicly disclosed. The decision on who will inherit the tiara will be made by the current head of the Spencer family or according to any arrangements specified in the family's estate planning.