Talented baking gurus diabetic cake help PLEASE!!

[NicNocJnr]

This is my first post on the baking board (because I didn't know you were here for ages! Have just spent an hour reading through...yum)

So I am official cake maker for my Nan's 70th birthday. No problems with that I thought but I have run into a bit of a bind -
Nan is diabetic and I am trying to find a cake that is not only sensible with refined sugar but carbs too.
I've decided to go with an almond cake with a sugar subsitiute, so far agave has come out on top although I am generally unconvinced (possibly just my own issue) unless anyone has a better idea (quite likely!) The whisked fatless sponge with sugar substitute was not good. When I say not good - my son cried, even I got a bit wobbly lipped!

Secondly it's a big birthday bash, really celebratory and all about her being queen for the day- she likes really highly decorated sponges so I'm trying to work out a way to make the almond cake look as special as a full on wedding style cake. This is not going too well. I've found lots of references to miracle whip and dry pudding mixtures from the US, which she just won't like even if I did get hold of some. Also using whipped cream - the problem with this is I can't be too heavy handed with fat as this is also an issue for her and can leave her feeling quite poorly due to some of the medication she takes.
Some icings I have tried with sugar substitutes have been, frankly, awful.

So now Im left with a request for a glitzy, special cake but with lower sugar, carbs and fat...which are the ingredients of both cake and frosting/icing.

I know that generally the recommendation is regular foods in sensible portions but...that's not going to happen
My Nan is type 2 and sensible portions are not her thing. I'm not the food police but her BG is all over the shop and I can't help but worry about the long term effects of this, particularly as she isn't in the most robust of health anyway. I just desperately want to provide something that she can have a portion of without it doing too much damage to her blood sugar so that the overall effects of her going a bit crazy on her birthday will be lessened. I'm actually also doing the rest of the menu and working the cake into this so we can try to avoid pushing her into a hyper.

For my next request: The moon!

Any help, hints or tips are welcomed with hugely open arms. I can make a great cake but I'm no pastry chef.
TIA

Hmm. With decoration, could you make a whipped ganache with diabetic chocolate?

Diabetic products aren't actually usually recomended for diabetics. Cake without sugar will be disgusting/won't work.

You can make chocolate cake substituting ground almonds for flour, but still need sugar/chocolate.

Most people who are diabetic just eat normal cake and portion control. However, if your nan doesn't keep her blood sugar's under control overall, the sort of birthday cake she has won't make a bit of difference really.

i have a tropical fruitcake recipe that has only the dry fruits and a banana as sweetener

i think the moon would be easier than try find a recipe thats low fat,carb and sugar!

Sorry didn't catch up yesterday I was working, thank you for the replies.

Midori- I hear you, and understand the usual advice. However In this circumstance having to scrape her off the floor due to cake overdose (with 5 DC and the rest of the family to be watching she will go mad whilst unobserved or assure another reletive she hasn't had any cake yet) is what will happen. Making the rest of the menu as diabetic friendly as I can is to try and reduce the load on her system but if I serve up normal cake she will be carted off to hospital at the end of the day she is so badly controlled and lives consantly one step away from a hyper. Welcome to my family we put the fun in dysfunctional! She gets wonderfully belligerent too!

Habbibu- I think lots of inedible decoration maybe? Thank you for the response x

Liveinazoo - That sounds very interesting - I will have a look for it, it's certainly helpful for ideas! And I doubt I will find one but if I do ever meet a wandering wizard I shall certainly spread the cake word!