Coworker Driving Me Nuts

So I had a new coworker start at my job about 3 weeks ago. From like the 3rd day we have been going back and forth with this teasing / kind of sarcastic banter. For example if I take something she printed from the copy machine, she will tell me to stop stealing her stuff or ask why I'm always stealing everything, then she smiles at me and laughs. She sits in my computer chair and pretends to be me. She came up and put hands on me from behind to scare me in the kitchen. We are constantly laughing all day long to the point where other people are noticing and saying we are having "too much fun". She is also very touchy, she is always playfully hitting my shoulder or tapping on my back. The other day I was sitting at her desk to fix something and she was standing behind me talking on the phone, she put her hands on the back of my chair and kept play hitting my shoulder, I made a joke and she literally put her hand over my mouth and laughed. Usually she leaves for lunch, but this past Friday she decided to have a pizza party, it was just the two of us, she ordered and paid for everything, and she stayed at the office the whole time with me and we watched Netflix on my computer while sitting 2 inches apart. When she gets close like that I just want to grab her because I find her very attractive. It is just driving me nuts and I need to vent, I know she is straight and just being friendly I guess, I'm not use to having such a relaxed and comfortable interaction with a coworker after only a couple weeks. I am finding it hard to focus on my work which is bad, any advice or whatever would help at this point :icon_sad: