Edit: For those wondering how this was made, here's a video tutorial I cooked up: www.youtube.com/watch?v=JYu6RO…
Ok... while she seems elaborate, she was a bit less problematic to work on than, say, Fluttershy or Pinkie Pie (Twilight having been the first real test)
Her tail being in sections rather than a mass (even if I did NOT make it in sections to animate) comes off much better I think
Plus, having her sword drawn and at the ready is something I had the idea to do ever since I thought of those 'Wanted' posters
She's essentially the Swordsmare of the group.
Magical seamstress with a franchised fashion boutique chain from Port Canterlot, Rarity had recently opened her latest store in Ponyville docks. Be it by luck, influence or plain hard work for her craft, she became known by the whole town as a generous pony. Great friends with her sponsor (And investor), Fancy Pants, she became even greater friends with his wife, Fleur de Lys.
In his last letter however, Fancy pants was fearing for his life as he was in defense of the Zebrican's way of life. He had apparently found out they were being traded as slaves in the sugar plantations.
Soon enough, crown guards were knocking at her door to arrest her and Fleur for conspiracy. Knowing she was innocent and bent on helping Fleur and her friend, she resisted arrest, showing off incredible skills with a sword.
Rarity can litterally thread a needle with that blade. With Twilight's help, she enchanted a special stone on a ring and the hilt of the sword to react only to Rarity's magic. It is nearly impossible for her to lose her grip on that weapon, except if she falls unconscious.
That makes many beleive that the spirit of her long-lost husband inhabits the sword and defends his wife, earning her the nickname of 'White Widow'.