Another mystery is solved:

It looks like she wore a historic court train from the year 1878 see more
Princess Clarissa is wearing the Furstenberg Laurel Leaf Tiara on her wedding in July 2024.
It’s the same tiara which are used from her mother Freiin Diana of Berlichingen in the year 1992 when she married Maximilian Joachim Prince to Fuerstenberg.
We have a match to the new sketches from Stefan Sterns Grafische Sammlung H.Nalbandian Eaubonne