Can she have soft goat cheese. I use this for my ds. There are some really subtly flavoured ones (not the usual rank goaty taste) in supermarkets. There are nice Welsh ones in a pyramid shaped box.
Otherwise I'd just do a butter icing and add a little greek yogurt to soften it. Perhaps some lemon juice and grated rind too.
Mmmm you've made me want to go and bake a carrot cake now.