Harley Quinn was an Arkham Asylum psychiatrist, who begged and eventually convinced her superiors to treat the Joker; Dr. Harleen Quinzel became obsessively fixated on her patient and believed herself to be in love with him. She helped him escape from confinement and took on her own criminal identity as Harley Quinn. Harley was a violent and unpredictable felon whose only motivation, beyond general mayhem, was achieving the Joker’s approval. Because of the Joker's cruel and mercurial nature, this in some ways made Harley just another one of his victims - albeit a very dangerous one.

she used to be very intelligent, responsible and caring… but it all changed once Harley accepted that she was in love with the Joker. She demonstrated extreme signs of regression, such as a higher pitch in her voice, becoming less assertive and appearing less intelligent - possibly to try to appeal to him. On a daily basis, Harley was cheerful and optimistic, but also sadistic and maniacal which she may have learned from the Joker. Unlike him, however, Harley often failed to reserve herself in combat and speech.

before the outbreak

Harley made her way to Bane's holding room in order to sedate him. The reason for this was to keep him quiet when the "visitors" arrived. With the prep work ready, Harley went to a control room to wait for the Joker's arrival. Once he was there, she would release their henchmen to takeover the island; then they would force Dr. Young to reveal where Titan was being produced, so they could build their army of Banes.*

beginning of outbreak

While Batman and the security guards escorted the Joker through the Intensive Treatment Centerof Arkham Asylum, Harley was already in the security control room waiting for his signal. As the Joker broke free, she opened the adjacent security field which allowed him to escape Batman and implemented his takeover of Arkham Asylum. Per the plan, Harley began releasing their thugs from all levels of the Asylum.

Currently

Harley Quinn had been tasked with keeping Batman at bay till the jokers party was finished. (AKA, probably something to take the Batman down). She was keeping Batman away again, with electrical flooring and enemies to try and take him down. But it’s Batman. It didn’t work. This, upset her. Her high-pitched, sing-songy tone spoke, unmistakably hers.

“He's done it again. I don't believe it. Im on my way now.”

she tells the Joker, but he responded from the tv.

“Oops. Change of plans, kiddo.”

“But I tried my best!”

she says in an almost whiny, annoyed tone. She knew what this meant. She won’t be getting to go to the party!! Oh she doesn’t like that… she loves the Joker! They’re partners in crime! He knows this all… and yet:

“Sorry, but there is no prize for second place. Im afraid you’re off the party list. Better luck next time”

the tv goes black. He doesn’t even feel bad for it. She left the control system for the electric flooring and ran at the bat, yelling:

“Die, you big, ugly bat!”

she did a cartwheel, a flip, and tried to kick his head and— was taken down almost immediately by Batman who didn’t even flinch. He had thrown her. He walked over, reaching a hand out but she hit him away.

“Hey! Hands off the merchandise!”

she tries to attack again, going for a punch. Expectedly, he put her to the ground. He scanned her finger prints, probably to help him get the asylum back in order. The Batman grabbed her and forced her into a cell. Harley tried to get out before it closed but to no avail, her hands gripping the thick cell bars. As the Batman left, she called out: “Damn! Well, he’ll get me out! You’ll see! Yeah… you’ll see…”

she almost seemed teary at the end. She sat down on the bed in the cell, and sobbed. She’s frustrated and upset.

“Mr. J will be back for me later. He's only messin' around…”

she says through tears.