A small headcanon of how she’d look like in my Next Generation timeline.
 
Instead of giving all of her powers to Twilight, Luna gives a third part to her and another third to Stheno, her oldest daughter. The last third part she keeps, in order to stay with her children and not get outlived by them.  
After giving up part of her powers, her body becomes like that of a regular mare, but with semi-immortality. Same goes with Celestia.  
Luna marries on Queen Novo, receiving herself the title of Consort Queen. The chestplate has a black aventurine stone on it, which allows her to become a seapony.  
She has a terrible relationship with Medusa, her youngest daughter, seeing as Medusa thinks of her mother as a weakling who went from being a powerful queen and a (formerly) enemy ponies would fear to a simple consort.  
I gave her white mane inspired on @/Orin331 and a few other people.  
She becomes a Pegasus because that’s the form she was born with before ascending to alicornhood (headcanon I share with a few other people).  
Stheno is the one who raises the Moon after her mother steps down.  
I may give her a crown in the future.
 

 
Base by ShiiBases | Character belongs to Hasbro | AU design by space-higanbana (don’t use without permission)