Oh! Hang on a minute.

Sorry, I'm not used to running pursuits in D&D, I read over the rules and found I made a mistake. 

Pursuers and quarries can dash (3 + Con mod) times per turn. So Siftus would be 120 feet in front of Elaranna. If Elaranna is still able to reach Siftus' space, she can attempt a grapple check to catch him. 

((Edit: Math))