Catwoman is a very fundamentals-based character. You can mash away with her, but you probably won't get far, and people will zone you out. You want to get familiar with the following:
Frame data (and what "safe" and "unsafe" mean)
Spacing
Whiff Punishing (that's a big one for here)
The concept of High/Low and Mixups
The concept of Oki and Vortexes
Wake ups and baiting/defending against Wakeups
Watching a good Catwoman will help a lot more than trying to figure this out on your own. To start, any videos you can find of Maxter or Krayzie playing Injustice will help. You can check Wednesday Night Fights archives @
http://twitch.tv/leveluplive or find the Toryuken archives at
http://twitch.tv/ralstoninstall in the Videos -> Past Broadcasts section of both channels.
Watch and try things, figure out what happened, and see how people deal with various situations. Good luck!