while starlight isn't a princess (but is potentially en route to becoming one, if twilight's mentorship says anything in reference to starlight's mentorship), sunset is highly predicted to be a princess of sorts.

sunset has magical wings in the newer iterations of her appearances (my past is not today and the end of Friendship Games), and shows almost celestia-like powers when facing off against others. so, although she's still technically a unicorn, she is portrayed as an alicorn (or will potentially become an alicorn)

she's potentially the princess of forgiveness!