Just had a really obvious thought about Terrigenesis.
Inhumanity is an inherited trait.
kamala's mum, dad or both are Inhumans too.
If neither of her parents are inhumans then, one or both of her parents are not her parents.
That leads to four possibilities...
1. Switched at birth. (Human error.)
2. Adoption/sperm donating/surrogacy. (Mum and Dad are part of the plan)
3. Mum had an affair. (Dirty mum!)
4 Golden Child Messiah sent off from a royal castle somewhere after life threatening circumstances (Snow white already! What if Bail Organna wanted a son?) to live in the relative safety of New Jersey. (mum and dad are trained assassins or palace guards.. The Powers of Matthew Starr?).