Who is she?

The memories Luca had to see didn't just stop at that time when the real Luca took those pills. She had a trip down the real Luca's memory lane, revealing and giving the answers the current Luca couldn't get answers no matter how she racked her brain. 

Luca found out many things; about the Fourth, the reason Luca had her eyes on Adam Crowell, and what sort of person the chief was. She also figured out the reason Luca dispersed her team. Although that last one was not a surprise. Luca already had guessed that she was trying to protect her team. 

Although many questions were left in that conclusion, such as the series of whys? Luca's team was strong and capable individuals who would protect themselves. They were people who didn't need Luca's protection. However, not when the Fourth was filled with far more dangerous people, like that person who held the actual power behind the Fourth.