I use the Dove's Farm White Spelt flour to make cakes for my SIL and Nieces - all gluten intolerant. It's not completely gluten free so no good if you need it to be that - but it's very very low in gluten and they are absolutely fine with it. It makes cakes, biscuits, pastry etc that you would just never know are not made with regular flour. Worth a try!
If it doesn't have to be a traditional birthday cake, google orange and almond cake James Martin (I'm not very good at links). It's on the BBC website. I've made this a couple times and it is pretty good.