Look man if a normal sized dude like Superman can tank nukes to the face without math explanations, why can't a super giantess?
Besides he already does have hella math explanations anyways.

Now that I think about it, there aren't enough "super" giantesses. They tend to be just regular girls who have become big or are naturally big, and that's the end of it, they don't usually have superpowers on top of it. But I'm like... why not?