I agree with what has been said above. Sometimes a smack is something that can be benificial. In your case it probably wasn't but hey, we are all human and make mistakes! Chances are you wont be hitting her again out of anger, and she wont hit your drink! She's probably forgotten ALLLLL about it
I slapped Jaidan across the face once when he kicked me in the shins. It was totally a reaction, I didn't think about it then slap I just did it automatically. I was so distraught that I had done that I cried for days when I thought about the look on his face I still get a little upset but hey I haven't done it again!
We all make mistakes