How do I make dessert that is low carb, non-dairy, and worth eating?

Oh, and I'll be bookmarking all of the fab suggestions here. I'm gonna try a panna cotta first. :)

Thanks for all of your help. I settled on a 2 dish solution. The no-carber made it easy by insisting the only thing that works is sugar-free jello so I'm going to class it up with some real whipped cream (sweetened with splenda) and a lite grating of zest on top. Man, it's HARD to dress up jello! For act 2 I'll be whipping up the YOGURT CAKE WITH PEAR AND DARK CHOCOLATE by fiveandspice, subbing out the regular yogurt for the coconut kind. We can then top it with the whipped cream, those of us who are allowed that is. Yay, everybody wins. Sort of. I mean come on, jello...

I think my Coconut-Lemon Macaroons probably qualify as low-carb, plus they're vegan so there's no diary worry:
http://food52.com/recipes/14717_coconutlemon_macaroons
I like to bring them as dessert because they're easy to transport, small servings, and free of just about anything allergenic.

You also may try poached pears or other fruit. That's usually pretty easy and totally looks like you slaved over it. Fruit crisps are also an option. You can use oats, nuts, brown sugar, and a little vegan butter for the topping and avoid flour altogether.

Also, I kind of specialize is catering for people with various restrictions and diets, so if you want any other tips or recipes, I'm happy to help :)

Here a couple of delicious recipes I've done in the past that have been a hit for a wide group of friends--

Coconut Layer Petit Fores- if transporting these from house to house, i recommend freezing them before and after transportation and they will be fine. http://icingoffthecake.blogspot.com/2012/01/triple-layer-coconut-petit-four.html

Cocoa Bean Cupcakes-- these cupcakes are flourless. the base is actually black beans--i know, the initial reaction is ew! black beans--but it's actually really delicious and moist! http://icingoffthecake.blogspot.com/2011/10/chocolate-halloween-cupcakes.html

Vanilla Bean Cake with Chocolate Frosting- http://icingoffthecake.blogspot.com/2011/10/classic-yellow-birthday-cake.html

Try a sabayon with fresh fruit.

As someone who has done low-carb before, I can say that I would have preferred to just skip dessert. She probably cannot eat any fruit (no, not even oranges) or sugar...panna cotta with splenda instead of sugar is possible depending on her level of restriction, but that wouldn't work for your dairy-free friend.
I'd check with her first on her diet because she might prefer to skip dessert entirely and then you just need to go dairy-free, which is easy.

This all sounds much better than what I had planned. I really like the apple cake idea, I have some dried apples that I have been wanting to use anyway. This is so hard. Dessert should be fun! ;)

That's tough, I would suggest making two separate desserts because for the low carb guest, dairy would actually be a good way to go. You can make a couer la creme served with preserves on the side or roasted fruit/ baked apples (as long as guest isn't super low carb as to avoid fruits) served with lightly sweetened cream on the side. For the dairy-free guest, how about meringues, an angel food cake, olive oil pound cake or a chocolate cake that is oil based. I have substituted oil in many cakes when dealing with dairy-free guests with great success. When substituting I do not go with delicate cakes, but apple cakes, banana, zucchini, etc. all do really well.

i love these thoughts but a quick note - fruit is a big no no on a low carb diet so depending how strict your friend is being, they might not work for her.

Baked fruit is always a good idea! Alton brown has a great recipe for stuffed baked apples (and you could do an unstuffed one for your low-carb friend if she's really stringent). Poached pears with some freshly whipped cream is also elegant and healthy. You could also bake a cake to go under the poached pears (something with cardamom or other spices) and just omit that for the pickier eaters.

You could do something with a nut butter (for a nice creamy richness without dairy) and chocolate that is 100% cocoa (thus no sugar) or just with cocoa powder. You could use ever so little of a sugarless sweetener if need be, but chocolate and nut butters taste pretty darn good all on their own! Something to play around with maybe.

What about a berry pavlova or a citrus panna cotta?