If Harley was merely a regular woman who dressed like a clown, she wouldn’t be that useful out in the field.
Although she’ll occasionally use standard firearms (there’s a brief shot of her using dual pistols in one of the Suicide Squad trailers), she prefers wielding more absurd-looking weapons, including her oversized mallet, a comically large pistol that shoots a cork, and that graffitied baseball bat she’s using in Suicide Squad.
While she doesn’t have any natural superpowers, she is a talented gymnast, so whenever she’s delivering a beatdown, it’s usually while jumping or doing backflips.
Fortunately, she has a particular skill set for taking on opponents.