How about a simple carrot cake with cream cheese frosting?
For decoration crush some cookies and pile the crumbs in your hand and while the icing is still wet apply them to the sides of the cake.
German chocolate with the yummy pecan and coconut cooked icing?
Of course you could do a white cake with white marshmallow icing (after icing cake make little waves or peaks on the top and brown either with a small torch which most people don't have or just stick it in the oven and use the broiler)
You mentioned she cannot have food dye but what about candy?
Either whole or crushed then added to the icing or sprinkled on top?
Ice cream cakes are so much fun and really easy.
Bake a pound cake recipe using an 8 inch round pan when done turn out onto the cooling rack then into the freezer when cooled (you can wrap in foil but this step is so short you can leave it bu** nekked.
Soften a quart of ice cream and pack into a plastic wrap lined pan of the same size (this can be done ahead)
When cake is cold and ice cream is refrozen remove them from freezer and either spread a thin layer of jam or use some of the icing for the filling then stack (ice cream on top).
Back to freezer, when the cake is stable (frozen solid) remove and ice with a simple butter and 10 powdered sugar icing (you need to move a bit quickly here lol)
Then back to freezer until about 10 min before serving time.
Anything look good?
Do you have a different idea?
Let me know and I will scrounge thru my recipes and post for you!
Welcome to Chef Talk @Milly Walter !!