Glad I came back to this thread! I read it yesterday and couldn't find her!
If anyone else is looking, search for "Rarity" under Hasbro's eBay store. It has an interesting item description that must be a typo!
Also Hasbro's eBay store has the Flash/Twilight 2-pack for $9.99 & free shipping. On HasbroToyShop.com it's sold out!
Oh you are right- she is REALLY hard to find! She actually doesn't even appear under the "Equestria Girls" section- you have to do a general search- so odd!
I figured "RRE" must stand for "Rainbow Rocks Edition."