This cosplayer is part-time streamer Baabuska. Based in Romania, Baabuska, also known as Ioana Sima, likes classic rock and dark fantasy. You can catch more of his cosplay over at her Instagram account.
In Dark Souls 3 the Fire Keeper tends the bonfire and helps the hero make their way through Lothric. She assists with levelling up and then healing the Dark Sigil.