I don't feel qualified to critique the image, but I think I can discuss dialogue and characterization.
1. If Harley had some way to knock out Supergirl w/ one kick, why was she so panicked in Me think I'm in trouble?
2. Supergirl seems to give up quickly. One kick and she's whimpering? She'd never faced a super-powered opponent before? The first part of her speech is overwrought, and everything starting w/ the first "(sob)" just seems wrong.
3. Harley lacks the twisted light-hearted yet macabre humor she usually has. See www.dorkly.com/post/76389/rev-…
for many good examples. If this is meant to be a different take on her it is so different, w/ no context, that it's disconcerting.
4. You misspelled "doesn't".
Supergirl's and Harley's speeches seem fairly long to happen in the split-second between impact of the kick and Supergirl going unconscious, but that's common in comics, so it's acceptable here.
I generally enjoy your work, and appreciate your patience in reading this critique. Thank you for giving me this opportunity.