"I'm really glad I met you, Dee..."
so it's kinda like a Harleen Quinzel and Joker situation. Allow me to explain.
A was just a high school student when the 'accident' happened. Someone's eye was stabbed with a dull pencil in the middle of class. The student who did it was none other than B. After being interrogated, they were released by reason of insanity and sent to a mental institute. The situation inspired A to study psychology and years later, while A's career was just taking off, they were sent to look at some of the criminals in a mental institute one of them being B. After they heard everything the people said, they freed the people locked up inside. Well some of them at least. B being one of the people.
P.S in case you don't know the Harley Quinn origin story, this is kind of a "love at first sight" well... not first but u get what I mean.