If you are uncomfortable with it, the first approach is to respond in a polite way that the behavior makes you uncomfortable. The coworker may not realize that what she is doing is bothering you, or may not realize that it COULD bother you. If the behavior continues, that is when you consider bringing up the issue with the boss or with HR.
She's probably not aware she's doing it or making you uncomfortable. Some people are just touchy/huggy types. There's nothing wrong unless you feel it's odd or gets inappropriate, I doubt it's going in that direction. She's probably excitable and happy.
i am one of those "touchy, feely" type people. I am aware, however, that some people become uncomfortable with that. (i am also a hugger). i always ask people if they prefer not to be touched or hugged, then try my best to honor their preference. i have on occasion touched someone in random conversation, and then immediately stopped and apologized. - consider that she has not realized that she is making you uncomfortable, and let her know in a nice way that this bothers you. maybe have her read this thread.