Do you have the add on called TomTom? I got my Unborn Val'kyr
s by using TomTom and making macros to set waypoints to each place where it can spawn and then just making the rounds of each spot. You can get TomTom from the Curse web site and there is a post in the comments section for the pet on Wowhead that lists the different spawn spots in sets to make macros. I know that there is also a post here somewhere that does that too, but am not sure where to find it.
FYI: if you engage her, and she has Unholy Ascension
in the 3rd slot, you can forfeit and she will respawn. Heal your team and reengage. Each time you do this, her abilities will be randomly chosen. You want to fight her when she has Haunt
instead. It is a royal pain to finally find one of these only to have it use Unholy Ascension
and just die!