This Ice Cold Tiara was originally designed to crown my daughter who loves Elsa from Frozen, but a color swap can easily shift it to an evil sorceress tiara, a princess crown or just the setting for the Purple Gem of Doom. It will print scaled down to 30% but I suggest 60% or larger for wearable durability. The file posted is sized for a queen. 60% scale is great for my 3 year old.
Tiara prints without supports, but rafts help with thin bottom edge. I needed supports and raft for the gem and found the facets to show up best printed horizontally, point down.
Gem may will need to be glued to be permanent, but that means you can't swap in fancy new gems later.