Unless you need a wide angle lens you might want to consider a Tamron SP 70-300mm F4-5.6 VC USD. I paid $449.00 with a $ 100.00 mail in rebate that I got back in two weeks.The rebate is still available. The lens performs excellent especially at its price point. You can cover a wider range of shots from what the 50mm doesn't cover for some longer distant. Just another option for you to consider.
The nikon version is a great choice as well, however I don't know if a 70300 is a great choice for her. It provides the zoom option, but for low light conditions with movement it just won't do well. Both the Nikon and tamron versions are decent in low light due to their superb VC and vr technologies, but it just doesn't sound like VC or vr is what she needs in a lot of instances (could be wrong though).
Jemstone, if you're feeling limited on the long end, something like a 70200mm f2.8 lend might be nice. The price for a nonnikon is still about 1200 or so I think? But that fits your description.
If you're feeling limited on the short end, the suggestion above about the 1750 f2.8 is good. I have been told the non VC tamron is far superior to the newer VC one, and the sigma version is good as well.
If you shoot at apertures at or above 4 and don't dip below that, there's the 16-85 nikkor, 17-70 f2.8f4, and some other even cheaper considerations such as the 18105. However, i would presume you'd be wanting a fast lens especially for wedding photography.
You may want to go the route of a 17-50 f2.8. I hear that's a great choice for your purposes.
Since you want zoom, you shoot weddings, and you want sharpness that may exceed what you get (and if we were assuming you are shooting very well right now), then you are getting into the big money zooms (17-55 or 1750 as well as the 70-200).
Another thought which is likely out of the picture is getting a higher megapixel camera. It shouldn't be necessary, but it sounds like you want more detail in that way?
Sorry, lots of theoretical knowledge I'm throwing around.