This is probably from another game that I have no clue about. There are so many MMORPGs lately that it’s really hard to keep up with everything that’s been going on as of late. I’m really glad a lot of the unknown cosplays are finally getting labeled and categorized properly.
So, guesses? My closest guess is that this is from Ragnarok, but other than that, your guess is as good as mine.
EDIT: By popular opinion, this is a cosplay of Valeera Sanguinar from World of Warcraft! Thanks to Maddog for the comment, and the anons who agreed with him! (Or is it her?)