Ahhh, I see.
I think her feet look solid and they bend at the correct parts. The clunkiness/stiffness might be fixed if you add a few more frames/tweens. You can get much smoother animation with more frames. If you're interested, you can look up "Animator's Survival Kit walk cycle" in google. It's a great book that breaks down animation and all it's principals. If you can find a digital copy of it, I can look up a few pages that pertain to your walk cycle.
And of course you can ask if you need pointers , I'd be more then glad to help ^_^