Your cake is awesome!!!
It doesn't look like it needs anything to me, but if you feel very strongly that it does, maybe another bow or a few of the larger roses like the ones that are on the board. I guess it all depends on how much time you have to make something else to add. Do you have time do do a small gumpaste crown or something like that? I see a lot of princess cakes with gumpaste mirrors also. HTH, and again great cake!!!
I think it looks great as it is - the only thing I could suggest is that the slipper be slightly higher at the back so it tilts forward a little to give it a bit more height - but I'm not sure how you could do that. Personally I would leave it as is, the cake looks lovely - nice to see a princess theme that isn't pink too!