dumb nerd theory: maybe ascended alicorn babies aren’t usually a thing,  like, shining and cadence both weren’t alicorns (cadence ascended)

and them having an alicorn baby was a shock 

however genetically, it might make more sense if you think about the fact that Twilight ascended to an alicorn as well. And she’s Shining’s sister. That means this potential is probably in their bloodline as well. So that’s double the ascension capability. 

Woops, baby ascended in the womb I guess