In The Wolverine we learn that Yukio is neither a real member of the Yashida family nor a mere employee, but she was an orphan found by Yashida when she was a child. When asked by Logan for the reasons she says that Mariko always had problems making friends. So it seems she was taken with them because she made friends with Mariko, which Shingen puts a bit more cold-hearted when he says something along the lines of (forgive me for not being word accurate):
You are a toy doll, a companion for a child who has outgrown you.
Which sounds a bit cold (and seems to be what Yukio thinks secretly, too), but sounds reasonable given that Yashida seems like a man that takes and gets whatever he wants.
But likewise Yashida is depicted right from the beginning as a man that fears his own death above all other things (even if this is emphasized more heavily towards the end). And from a story viewpoint Yukio's mutant power to predict other peoples' deaths doesn't serve much more than to classify her even more as an outcast (and maybe to raise the tension by falsely predicting Logan's death).
So are there any hints that she wasn't "adopted" just to provide a friend to Mariko, but for Yashida to constantly have someone around him who could warn him of his death? And was this an additional device to emphasize his constant fear of death and thus another hint to his actual plans? Or am I just over-interpreting things here?
(While it may be that this was intentionally left open for interpretation, there could also be additional hints suggesting the one over the other).