Didn't see a thread about this yet, which surprised me.
From Newtype December 2013 Issues.
Type Moon announced new manga of Fate Extra series called “Fate/Extra CCC: Fox Tail”. It’s alternative route of Tamamo no Mae. The plot synopsis is given further explanation about Tamamo’s background of relationship between her and Amaterasu.
Takeuchi stated that Tamamo look-alike is new servant was scrapped in the game, supposedly focus on Sakura Labyrith. Until then Takeuchi wanted to finish the design and put her in the manga instead. She will debut in the manga alongside with unused Sakura Five such as Violet, Kazudrop & Kingprotea from Fate/Extra Material