The more unstable ones are beginning to snap mentally.
I don't know if you read the clever and gripping WORLD WAR Z by Max Brooks. It is one of the neatest takes I have ever seen on the zombie genre.
Brooks had a chapter dedicated to soldiers reporting the encounters with "quislings." These were sensitive and weak people so driven mad with horror and nervous exhaustion they began to try to fall in with the zombies and came to believe they were zombies. This is actually a common phenomenon seen in R-selected evolutionary coping strategies - defecting to the side that is winning. The soldiers said they were the most violent, savage and cunning of all the opponents, sometimes even more dangerous than the zombies themselves. They were hopelessly insane and efforts after the zombie wars found it was nearly impossible to rehabilitate them.
These people are quislings whose mind has snapped at the strain of the bizarre, hostile polyglot of strangers attacking them from all sides at once on what they believed was safe home territory. Since it is forbidden for them to even show signs of fear, they instead just go nuts and become that which they fear most. It is the only thing that can alleviate their raw terror.
You're going to see a lot more of this, mark my words. One out of two people has the potential to go even crazier than this woman.