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. :)