User blog comment:Darkcloud1111/Good Idea, Bad Idea~Mountain Glenn/@comment-24792226-20141015144238/@comment-3146930-20141015223455

I actually answered this question on the episode page, so I'm going to be lazy and just copy/paste that answer over here:

We have seen from the fight with the Nevermore and Death Stalker that when under pressure, Ruby may have a harder time controlling her Semblance as she could have easily used it to out-speed the Death Stalker following her, but didn't. In this episode, Ruby had just fallen down an unknown height and is currently standing on the edge of a very large cliff. The first thing she reaches for when she lands is her head, possibly signifying she was a bit disoriented by the fall. Then two guards immediately show up and she finds she is missing her weapon. Using her speed that close to a cliff may have been dangerous as the wrong move could send her off. The WF members also are on her in a matter of moments, really limiting her options. Her speed tires her out as shown with Penny and Ruby doesn't know how many people she will have to fight, so maybe she was conserving energy.