Catwoman was sticking to the rooftops. There were still a few zombies left and she wanted nothing to do with them, so the rooftops were safe enough.
She looked out over The City from the rooftop of the museum when a figure down below caught her eye. When the person went in the back door and didn't come back out, she was curious to see who else would have broken into the museum and so she picked the lock and headed down the stairs of the museum, being very careful to be as silent as possible.