In the second to last episode, we find out that Mona had killed Charlotte DiLaurentis, Ali's transgender sister. She goes to Radley, the mental institution, and is released in the final episode, which is when she goes to live with Hanna and Caleb. We see a figure in a hoodie sneaking around Rosewood that night; we see that it's Melissa, Spencer's sister. However, it turns out to be a mask and underneath is Mona. At this point, it's looking like she's going back to her psycho Mona ways. But she helps the gang find Spencer and Ezra when they go missing. After that, we see that Mona is working in trinket shop in Paris and has a new man in her life. When she walks downstairs, there's a dollhouse laid out, a replica of real life, as she has trapped Mary and Alex Drake in a life-size dollhouse. Leave it to Mona — she always has good intentions.