Obvious reason
She was wanted in seventeen countries for espionage. Jennifer was shocked. Living the double life, trying to hide something beneath the eyes, there was more to what could have happened that no one else could explain but the footage served its purpose. There was something happening in the background which gave them the clarity they needed.
The reason she infiltrated the lives of Jennifer and Julian is that Julian works as the director of the national security company. He has access to the entire national security grid. Elizabeth had probably been hired by a rival company to leak secrets. At night she wiped the footage and tried cracking Julian’s computer.