Following MM is a bit stiff and not very flexible. Every technique is an observed behavior from a successful natural. So ask yourself how you can make every technique a part of who you are, naturally and more fluid.

Anyway, to answer your question... Depending on how you feel about the girl (you should always be congruent, remember?), your response to her touch should be accordingly. If you like her touch (which is a normal thing to do in the beginning), then smile back to her and give her some appropriate touch back (or even hug her if you want). This is a positive feedback on her IOI, which will probably make her escalate her IOIs. You just don't want to be too obvious yourself, so never give her more IOIs than you receive from her. If you feel she is too much and annoying (if she does it too many times, too much etc), push her away. If you want to be more conscious in your actions, try to be a little random in your respons. Pull sometimes, push sometimes ("oh, you just can't leave me alone, can you?" with a smile).