User blog comment:Zathronas/Analysis by an author: Volume 2 episode 3/@comment-2006510-20140808072655/@comment-24218038-20140809035111

That's assuming she had anything left to stop. I'm pretty sure she didn't expect Penny to weight that much.

Deer in the headlight: name one in RWBY. But besides that, RWBY semblance is speed, she would need wicked reaction time to go with it or she wouldn't be able to control her speed.