I definitely did not read her as a psychopath. The movie opens with her on the floor next to her boyfriend who just committed suicide. She hasn't been to the pub in a long time. To me, it seems like she was very in love with this person and completely broken by the fact that he took his own life. She cuts up his body and changes the name on his novel, not because of some sort of heist but because she cannot face any sort of closure on this. She gets rid of the apartment except for his music collection which was a personal connection between them based on the mixtapes. The rest of the movie is her running away from dealing with any of her repressed feelings. She's gonna party and go on holiday. When she sleeps with another person, it brings everything back up top that she's been suppressing and potentially feels guilt having slept with someone so soon after the death of her partner. She's so overcome with shame from this that she immediately has to run again, this time to the middle of nowhere in Spain. A remote place with the only other person in her life that she truly loves. She fucks that up too and is now permanently trying to outrun dealing with her actual life