The D3100 is a very capable camera. I would suggest that she use P (Program) mode as opposed to Auto (the one in green). Then, go to the menu, find ISO sensitivity settings and turn the Auto ISO sensitivity control On and choose ISO sensitivity 100, maximum Sensitivity 3200 and Minimum shutter speed either 1/125 or 1/160. IMO, that's an ideal point and shoot starting point. I would also pick either C or S as opposed to A for the focus settings.
Edit: One other suggestion. Don't use her camera under any circumstances since it's not likely that you will ever shoot film again after the experience.