A well done piece. I don't like the face. It looks very... odd. The nose, mouth, and brow look wrong to me. I'm a piss poor artist so I have trouble putting my finger on it. Something just seems off. The pose is neat. Unless the Hammer is paper mache that is a truly unrealistic way to hold it. But as a whole the piece is far superior to anything I could make. I do like the subtle background. Good job.

Art's perfect, no doubt about that. But I never really favored Harley as a character, as opposed to the THOUSANDS of people that see her as some type of heavenly deity.

Alright, "proper" review time yeah?
Now, I really admire the physique you've given her, like in terms of proportion. I can never get that right, so respect to that. Despite the simplicity, I like how you have an exact light source for the shading, a lot of people, including me, struggle to keep the shading around one specific light source, whether it's seen or unseen in the picture. To be honest, the only quarrel I can well up (which is really just subjective and petty more than anything) is the line thickness, feels a bit too blocky and rounded for a character like Harley Quinn.
Which Batman inspired you to make this by the way? The 'Arkham City' game redesign was horrible! She looked like a young teen trying to live up to her version of "hardcore". There's often a fine line between cheeky looking and the childish/immature portrayal which comes off as making the artist seem a tad creepy. You, my friend, didn't cross that line.
Hope this review proves helpful, thanks man. :)

She has a very Juri smile. (Juri from ssf4) Nice art.

As a big Harley Quinn fan, I approve of this!