She does exist, unknown to the world. Actually, the mention of Madoka in the teaser headline made the idea of a prequel a bit weird, since even if Mami and Kyouko knew each other, they obviously went separate ways long before the whole Groundhog Month. It would have had to be different stories, one about Oriko/Mami/Kyouko, the other about Madoka [and, judging by the Vol 2 cover, Homura?].
The reason why everybody considered it a prequel was because nobody thought Mami and Kyouko would have
really lived on in the end.
And if it is a sequel... Except speculahs. Mad speculahs. Oriko becoming a reincarnated Madoka or her medium. Or Madoka becoming able to roam around like Hamlet's father. Or whatever else.
