How much film and development are you talking? If your friend has a good SLR with a flash unit I wouldn’t consider using anything else. I think it is around five bucks extra to get a CD with the development of 36 photos so you can view them on the computer and TV.
If you absolutely want to use the S9100 go buy a flash attachment if you don’t already have one. You can get a decent automatic bounce flash for $30 and you will take better flash photos for the rest of the time you own the camera. For a little more money you can get better power. Ask what people are using on the Fuji forums.
Make sure she has the flash for the practice shots. Automatic flash units are easy enough to use once they are set up. But not really automatic like a TTL dedicated unit.
You can take beautiful outdoor shots in sunshine as long as you don’t have the subjects squinting into the sun and use fill flash. Even the built-in flash on the camera will work for that within range.
You want pictures of everything. Especially the ceremony regardless of how simple.
Go through some of these and get some ideas:
http://search.pbase.com/search?q=wedding&c=sp Or do a search for professional sites and see what they are doing.
I got a diffuser for my flash attachment for when I didn’t have a low white ceiling to bounce from. I think it was in the $20 range and makes flash portraits look nicer. You don’t need it, but you will like the photos a lot better with a flash attachment on your camera regardless of whether it has a diffuser.