She'd debated being Cassandra, or Batgirl when she posted to Faith. In the end, the other woman needed to know Batgirl more than Cassandra, if she was going to help with the threat that was fast approaching. It was simply a matter of saying 'Computer, search.' and she soon knew where she was meeting the woman. Her usual mode of transportation, her Batcycle, got her to the park for dark.
If there was one thing she was good at, it was creeping around undetected in the shadows. She had no idea what a Slayers senses were like though, so it was very possible that Faith heard her silent approach.
When she spotted the woman, her breathing, movement and expressions suggested annoyance or anger. Something was bugging her. But that was obvious from the second she said she needed to hit something. Her day had gone from alright, to sour the second she had decided to talk to Talia. Batgirl didn't like the idea of being used as a weapon against Lady Shiva. She might have been the only person in their world to have ever defeated her, and she might have been the worst mother of all time, but Cassandra would not allow herself to be used against her.
"Bad day?" she asked, approaching the Slayer in a black leather outfit, not once inch of skin showing. As much as you acted one way, your movements would always suggest something else.