Who is this in Fairy Tail? I am wondering as I cannot remember seeing her before in Fairy Tail. Can someone help? Am I missing something?
This is Cosmos, who first appears in chapter 307 of the manga. She is one of the Garou Knights. The image that you have is a colored image of her from Deviantart by SeireiART.

She has plant magic, which is why the Deviantart picture of her refers to her as the Flower Executioner. In chapter 308 she creates a giant flower.