Jim, just a suggestion, a 3100 is definitely not the right upgrade path. the D80 has way more manual controls than either a 3000 or 5000 series camera. Of the newer cameras the 7000 is the only one with more manual controls than a D80. I would suggest your daughter takes some classes and learns more about her camera. A D90 also has better controls than a D80, I have one and love it, but it is being phased out at this point and replaced with the D7000
This was just the post I was looking for. My daughter has the D80 (I think) and wants to step up to more manual features, rather than simply point and shoot. Already familiar with Nikon layout - she selected the 3100 for her next step up but I was wondering what the differences were with the 5100. I agree with the swivel ability of the screen. She does a lot of self and group portraits that I think is needed for such situations. Anyhoo, I am glad I found you two talking about this.
The D3100 is lighter and smaller-but not by much either way. The swivel screen is a big deal; it definitely increases the functionality of the camera, e.g., self-portraits, low and overhead shots, and video. Image quality is a wash. Yes, the D5100 has better dynamic range, but that will only matter if you shoot RAW and post-process. The D3100 is significantly more user friendly for noobies. Its controls are better arranged and better thought out, so it won't be hard to quickly get started. The D5100 has a few more capabilities that advanced beginners and enthusiasts on a budget will appreciate. Bracketing for HDR shooting is the feature that stands out. There are also a few more options in video including the option for an external mic on the D5100.
As an enthusiast looking for a small, compact, economical camera to complement my enthusiast-level Canon cameras, I opted for the D5100 instead of one of the Canon Rebel series (I've owned three and finally concluded that the Rebel AF was inadequate for my needs). However, making a recommendation to someone who had never used a DSLR or SLR, and just wants to get better pictures of family and friends, I would unequivocally recommend the D3100. However, for someone who thought that photography might become a serious hobby, the D5100 is the obvious step-up choice to get instead of the D3100.
Another consideration is how it feels in your hands. Both cameras are very small for DSLRs. Users with big hands are well-advised to try these cameras before buying. I've heard lots of complaints that these cameras are simply too small to comfortably use.
Well the D5100 cost more so it is a better camera. The main thing is the D5100 use the D7000 sensor, which is best in high ISO and lowlight over any other APS-C dslr (that include any canon like the T3i 60d, even 7D which all used the same old sensor). It has a swivel screen over the D3100. It is a little faster in continuous shooting at 4 fps vs 3 of the D3100, not really a big deal. Otherwise from the major reason here it is the same in a lot on most other specs.