Why I couldn't enjoy this mess of a film

The first 40 minutes of the film were excellent. It was basically a character piece and we were following around a desperate character who was unsure what she was doing, but was heavily motivated by getting money because she was broke. She was a likable character who was sarcastic but still cool. Once she gets date raped by her professor, the character of Mary does a COMPLETELE 180. The film DRASTICALLY changed from here on out. After getting date raped, she decides to torture him and tells him shes changing specialties and going into body modification. She does jobs out of her apartment, has a security guard and decides to closely work with the guy from the club.

Did I miss something? Where the hell did all this suddenly come from? This film just did a complete 180. She only did two jobs before and after both times she was pretty freaked out and taken back by it because they were so strange. To have the character drastically change from normal to psycho in a minute like that just doesn't make any sense. I am all for twists, but this just came across as completely random. I felt like I was watching a totally different film. Mary in the first 40 minutes of the film is drastically different from Mary in the remainder of the film. There is no transition.

The rest of the film was all over the place. I had no idea what was going on because the character of Mary just seemed to be all over the place. She goes back to helping out Beatress, then to hanging out at the club and becomes closer with Billy and develops feelings for him out of nowhere. I just didn't know what was going on or what to follow.