I obviously would not recommend hitting her, regardless of whether it is playing or not - that's pretty much common sense. Hitting is a good sign when you tease her, she can take a joke. I would take things to the next level, start possibly holding her hand. Or better yet, do something such as the following. Take baby steps of physical closeness - as it seems you have no problem talking with her and creating rapport.
This example may not apply to you, but it will help you understand the concepts needed to build physical closeness towards her... and will create ATTRACTION between the 2 of you.
Let's say you were going out with her to the movies as friends, and as you open the door of your car to take her out, you give out your hand for her to hold. However, when you grab her hand, hold on to it for a little longer than normal. BUT the moment you feel she will pull away, YOU need to pull away and make a ****y remark with a smirk on your face such as, "Hey! No holding hands this early!" And you say this as if it was her idea to hold onto her hand longer than normal. Little steps such as this one will create physical attraction, which is what women want went they hit you when you tease them. Try this out, and tell me what happens.
Nick.