If, a term purposefully penned by many here offering sage and considered advice, rickryan "believes her actions are having a sufficient effect on his reputation" pacifist methods of response allow the damage to progress and may provide evidence of future claims of habitual, contributory passiveness.
How this thread became mine, I'll never understand. That said, I think Bob has missed (yet again) my point. Bob's approach, from my reading of it, is to quietly contact the client and try to pacify/resolve the issue. He's hoping they will remove their online posting(s). I believe he works mostly with repeat, corporate customers. He's not a wedding jock, which is a different world.
My experience, based on 80-100 weddings per year, is that these girls are mostly young and immature. Whenever they post a bad review, it's a toss-up whether it actually is something that the DJ did wrong. It's often just a perceived disappointment with their day and by golly SOMEBODY is going to pay for it. The DJ, often times, is at the bottom of the totem pole and is on the receiving end, regardless of who actually is to blame. It's also about 90% certain, that her online complaint is going to be inflammatory and most of it will be made up. She's not wanting to pacified. She's either trying to extort money back from the DJ or she's just trying to do as much damage as possible. Fortunately, those reviews often are pretty easy to see through and most people realize when it's just a crazy bridezilla. The trick here isn't to try and erase the slight. The trick her is to exploit it. If you call her, you're going to get blasted and you'll likely strengthen her resolve, ending up with her seeking out other avenues of dinging you. I believe the best course of action is to wait a few days, to let her cool down. After that, give a thoughtful, polite response. Keep it short, sweet, non-combative (as possible), then thank her (yes, fake it) for her "valuable feedback which helps us to make things better for the next client". As long as you don't start having substantial numbers of bad reviews (I currently have 2 bad out of 105 total), you'll occasionally get feedback from prospects that they called you precisely because of how you dealt with "that crazy zilla". That demonstration of professionalism, in the face of adversity, will work far more in your favor than her complaint ever will against you. Personally, I want a couple of bad reviews. In addition to the above benefit, it makes the other 98% more believable.