@Millennial Dan  
looks it up
 
By jove you’re right!  
Good call sir, I think my theory needs some refining…

@ED-SKaR  
Celestia wore a big honkin crown for Twilight’s coronation ceremony.

Neither are crowns, both are tiaras!
 
The initial element of Magic was mounted on the studded tiara, then when she became a princess the element was remounted onto her regal tiara, signifying her princessdom.
 
 
Interestingly they keep the tiaras consistent between all the princesses, and the only crown show (afaik) is on the head of Queen Chrysalis
 
King Sobras head gear is arguably a crown or a tiara, we never get to see the back of it, because it’s under his mane. IMO it has the appearace of a thin crown, prevalant in many cultures for male leaders

Her latest crown is perfect though.  
Perfect to poke people in their eyes.

@Millennial Dan  
At any rate, it’s a moot point now because all of the Elements of Harmony and their pieces of jewelry were absorbed into the Tree of Harmony. All Twilight has now is her princess crown, with a non-functional gem inside it.

@Zennistrad  
Perhaps, although OneOverTwo’s comment may be as reasonable an explanation as any. They simply removed the gem, which contains the actual power or whatever, and mounted it on a new base.

@Millennial Dan
 
It’s magic, you ain’t gotta explain shit.

@SeanNH  
Actually, they’re both the Element of Magic. For some reason no one’s yet cleared up, it underwent a redesign.

I never even noticed her element crown thingy was different than her princess one.

And obviously all the power is contained in the gem.