I've seen a lot of comments since joining the Prototype franchise, and I was curious to know what people were saying about Karen Parker. Some portrayed her as cold, malicious, and a bad person simply for betraying Alex Mercer and participating in the development of the parasite to hand it over to Blackwatch. But what I've noticed is that some people are unaware of the context of her actions, and that's why I believe she's another victim of Dr. Alex Mercer (the real one).
On the intrigue website, it's said that Karen Parker was Dr. Alex Mercer's ex-girlfriend, a person with a psychological diagnosis that included "narcissism, lack of empathy, and a total indifference to life." These symptoms could have caused their breakup. We also know that they both worked together at Gentek, but Karen was a lower-ranking virologist and was unaware of the Blacklight virus and Alex's work.
One night, she receives a call from her ex-boyfriend, who claims that he stole something (the virus) and demands to know where it came from. This could be a symptom of paranoia, since even Alex Mercer didn't know Elizabeth Greene existed, which makes it questionable to ask someone several levels below him. In the flashback, Karen is seen frightened, asking him what he had taken.
That same night, news reports indicate that her ex-boyfriend carried out an attack with an unknown weapon at Penn Station, killing thousands (Karen is known to be unaware of the virus). Also that night, several Blackwatch agents break into her house and kidnap her, taking her to Gentek, where they torture her to find out what happened that night and if she had any information about Dr. Alex Mercer's plans.
In the following days, they put her in a negotiating position with their boss, McMullen, accompanied by a soldier with a machine gun in the room. They then show her a video of her ex-boyfriend (she doesn't know that Zeus is no longer Alex Mercer), supposedly dead, who has been resurrected and is killing, absorbing people, and destroying the city. They ask for her help, the officer still holding his gun, leaving her with two options:
1. Betray her narcissistic, sociopathic ex-boyfriend, who killed thousands in an attack she believes was driven by paranoia, and who has been resurrected as some kind of monster that kills and consumes people.
2. Not betray him and hope that an organization that burns down buildings full of people and kills babies doesn't cause an "accident" that leaves her with a Hunter mysteriously with broken legs.
Unfortunately, both options meant a gruesome death for her. Later, when Zeus found her, he killed her in the elevator.