see through (someone)

Translations
видеть (кого-то) насквозь
They could see through her and knew she was pretending to be someone she wasn't.
Они могли видеть её насквозь и знали, что она притворяется кем-то, кем не является.
Definitions
To understand someone's true motives, intentions, or character, especially when they are trying to hide them or be deceptive.