Must be the Order of the Elephant, which she received in 1961.
: 2: could be that HH is not actual owning : this fringe tiara... I am sure we would have : seen it on her again + perhaps on one of her : heirs... had it actually been owned by : her...?
There are only few pictures around of Princess Viggo, so she could well have worn it other times than we know of. Actually I have just now seen that she wore the fringe tiara also for the pre-wedding gala in Athens.