Ok guys. Now that the origin is finally complete. Let's talk about the origin.
To me, I thought the origin was a little rushed when it came to focusing on Harley's past but the origin showed a series of triggers that had everything to do with Harley snapping and going to the Joker.
Harleen is now presented as a good model student originated from NYC in the past whose been awarded honors, scholarships, the whole nine yards. She has also admitted that she has been a series of relationships possibly before the Joker came into her life so she is no stranger when it comes to love.
This Harleen is very different to the old Harleen in a lot of ways as she is very assertive and will not be afraid to defend herself if needed but also very professional and attempts to keep it strictly that way.
However, this is where those attempts get pushed to the edge.
Joker somehow gets his hands on Harleen Quinzel's profile and background and starts to really push her buttons, especially when it comes to a trauma that happened in her early life with her father's death at the hands of a corrupt wealthy business man who managed to pull a string of connections to be able to get away with murder and with Harleen's resentment and sorrow left to grow against the injustice. Joker makes the first attempt to win over Harleen's loyalty by giving her the bloody,diamond-encrusted ring-clad finger of the wealthy man in the assumption that Joker killed him. Whether this man is really dead or not, it is not yet known but Harleen seems convinced that he killed him and seemed grateful that he did the deed even if she looked like she was trying to hold in her emotions as she was crying.
As the story goes on, it is shown that she has admitted her personal feelings about Joker towards her supervisor and needlessly to say, she wasn't pleased that she was starting to like the Joker. During the argument, Harleen notices fallen papers on the floor which she recognized as her research papers on the Joker. She then figures out that her supervisor was stealing her research despite how harshly her supervisor has treated her during her employment in Arkham and this is the straw that breaks the camel's back with Harleen as she snaps violently and then frees the Joker out of an assumed gratitude for him and even agrees to take the Joker's invitation to come with him somewhere.
When they get there, that's when things start to get really horrific for Harleen as she finally realizes what she has done and started to have second thoughts about being with the Joker. As she voiced her want of leaving, Joker throws her into a vat of chemicals and watched her in merry glee as she screamed and begged for help as she eventually drowns. After he checks to see the remains of his next victim, he is in shock to see her still alive only with two-toned hair and bleached skin with a mental state as unstable as his own. As Harleen takes in the new sensation of her new form, Joker amusingly gives her a hand to pull her out of the vat only to be forced down into a kiss by the now lovestruck and newly dubbed Harley Quinn.
IMO, it's better than Mad Love because we finally see what factors were responsible for Harley going crazy but with the chemical vat as a way to reinforce her loyalty to him and aid him in causing chaos in Gotham.