I'm sensitive to the blood sugar effects of sugar, so I really like agave nectar. It's glycemic index is something like 15, but has the same calories as table sugar. To me it tastes just like a simple syrup, very mild, so it's a good substitute for sugar. It's sweeter, so you can use less of it. There is a dark and light variety, but I believe they taste the same. I've read that you can use it in any recipe that calls for honey.
I also read that in jams, you can't substitute it for all of the sugar because it won't gel right, but the Pomona's Pectin would help with that(they recommend using agave nectar on their website). You should follow a recipe that specifically calls for honey or agave, so you get the exact ratio right. I did find some recipes for jams made with all honey, so you could probably follow those and use the agave.
http://www.motherearthnews.com/DIY/1973 ... With_Honey
Here is one recipe for apple jelly that uses agave:
http://www.blueagavenectar.com/AgaveRec ... mjelly.htm
I don't like chemical sugar substitutes, and while searching for natural sweetener ideas a while back I found this website:
http://www.sweetsavvy.com/
It's a great site that has lots of info on all the natural sweeteners, including agave, along with plenty of recipes for each kind. The lady-Deborah Lynn Dadd-researched each sweetner and developed the recipes herself. Your friend might find some good ideas for naturally sweetened desserts there.
Good luck!