Your picture is much better!
I'm now absolutely convinced that the tiara is the same. And your explanation about traveling with a valuable tiara being difficult sounds plausible. Also, wearing a wedding tiara was not as fashionable in the 80s and 90s as it is nowadays.
I also think that it might be an Arenberg heirloom. AD Otto and Regina didn't have many jewels left to leave to her children, and I have never seen a similar tiara on another Habsburg lady. On the other hand, I have never seen a picture of another Arenberg lady with it, so this is just a speculation.
Btw, I sometimes thought that AD Kathleen didn't wear a tiara because she was getting married in the US.