This mob was by far the hardest for me to spawn. I spent almost a full day killing the same three static sand snakes thinking these would be PH's - no joy.
Then I looked on Magelo and discovered she spawns at various places - too many to be a static spawn. So, it must be a roaming mob that is the PH. Trouble was, there were no sand snakes left on track.
Turns out this is one of those weird zone when killing a mob doesn't necessarily mean it will respawn as the same mob.
So, I began slaughtering all of the roaming mobs on the middle to north part of the island. Within 15 minutes there were about 10 sand snakes on track and after an hour or so of killing them and many other roamers, she finally spawned.