User blog comment:Project Predacon/Volume 2: Post Credits Scene Analysis/@comment-3146930-20141031002734/@comment-3146930-20141031003604

Based on the Grimm mask, I would say she is a Faunus in the White Fang that met Yang's father before joining. It wouldn't be that hard to believe considering some of the things the crew have said about Faunus and Humans being able to breed, as well as someone that is half-Faunus maybe not knowing it. Also Yang and Ruby grew up on a small island that probably didn't treat Faunus as badly as we see some people do. It is even possible she left to fight for equality and to prevent Yang from knowing she was half-Faunus, as people might treat her badly if they found out once she left the island.