There was a quantum anomaly in Argentina that created Ava’s molecular disequilibrium.
Ava relates, via flashback, the story of the explosion that gave her powers and also killed her parents.
The Collier Metals factory in Atlanta served as both the exteriors and interiors for this Argentinian factory. This is the same building that played Terminus in The Walking Dead.
(Ant-Man & The Wasp, 2018)