I was surprised it took so long for Mary's wedding tiara to appear...... I actually don't mind it, you know, before the glue gun came out! Especially when compared to Snakey's and Sophie's disasters. But Mary really was a victim of Joachim and Alex's problems, otherwise she may have been given a better tiara - perhaps even the floral now loaned to Marie. It's certainly nicer than either Vic or Madde's 18th tiaras, which are just sad little things!
With regard to whether Mary will insist Marie give hers back, it belongs to the Crown, so it would have to be Fred's call (and he wouldn't)...... Same with Daisy's tiaras, she gets no say in who they go to (well a couple that are her personal property yes) but the couple of major ones go to the new Queen...... Which at the moment would be Mary..... I would suspect she would bequeath her personal ones to her granddaughters
The tiara Marie wears is actually apart of Margrethe's personal collection, so she might leave it to Joachim along with others. I'd say most of her personal jewels will probably go to her grandkids(tiaras and such) to Isabella and perhaps Josie.