The Dame MIGHT be exaggerating. In 5E, Aasimar are a PC race notable for being the equal opposites of Tieflings, and having radiant and necrotic resistance.
Two resists? Little busted.
Lore in most games I've played with aasimar in them, they're a rare product of humans, and the insinuation is that a celestial or God touched the child somehow, in an allusion to the Immaculate Conception.
I haven't looked at 5e, but hell, Pathfinder 1e has at least half a dozen types of tiefling and aasimar, for each type of celestial or abyssal that made it.
Regardless, if her stat block isnt "correct", it's on purpose.
