Ok I have a new theory on the identity of mystery portal sword woman from the train.
*ahem*
Ok so the last episode's credits names mystery woman as Raven Branwen, which is Qrow's last name. Implying some family relation to the Rose/Xio Longs. Now Ruby and Yang's father is named Taiyang Xio Long, so not only does Yang go by her father's last name but also it means that Qrow cannot be related to the sister's through their father. Ruby must also go by her Mother's maiden name, "Rose" which means Qrow also cannot be related through Ruby's mother. This leaves only Yang's mother as the person through whom Qrow is related to the girls. Which would imply that Yang's Mother's maiden name is Branwen.
Therefore, Raven Branwen (Mystery Woman) can only be, through process of elimination, Yang's mother.