You are right, ahanks, and welcome to TRF! It was the Isenburg floral tiara.
The discussion above is from early 2011. So that was before Princess Sophie of Isenburg got married to Georg-Friedrich of Prussia. In the course of that wedding better pictures and information about the Isenburg tiara surfaced. So with those new pictures we can be quite sure that Princess Katharina wore the Isenburg floral tiara as well.
I haven't seen pictures from the reception. Did Princess Katharina really switch tiaras? I know that her sister Sophie did in 2011, she also wore the Prussian meander tiara.
I wish I knew, but I can only guess. And my guess is, that AD Lorenz, as eldest son, will at least inherit the large tiara, possibly also the emerald necklace. Maybe the second tiara will go to AD Martin.