User blog comment:B214/Volume 22 spoilers/@comment-189.14.202.69-20161016140306/@comment-30006382-20161016191425

Could be possible, but you gotta remember that she has higher demonic powers than the average high-class devil. Tiamat, also known as the strongest dragon king, has strenght comparable to a ultimate devil - maou. Had her description not been that precise, she could have been anyone. Because of that, her being a newcomer is the most plausible case.