OOC: Hmm. I think this means not only can I never catch her, but anyone whose movement rate is greater than 1/2 of their opponents rate can never be caught. This provokes an interesting "is that the intent" problem. Consider that for opponent movement rate M, as long as I have movement rate M/2+5", I can move away and ready a MEA to move away from the opponent as they approach. As long as I have M/2+5", then the combination of my move + readied move will be greater than their move. The opponent can't charge to rectify this, since I can ready a move away at an angle that will break the straight line requirement of the charge. The only other cap on the equation is to have an move rate great enough to pin anyone within the current environment, even after the secondary move. So a movement of at least 60"+opponent_move would allow you to center yourself at 60N60E, move to the opponent, then be able to follow after the interrupt of the readied retreat.
Did I miss anything in the analysis?
If not, the Sacred Watcher will chase the Gynosphinx until the draw elapses.