this is just my advice and I am sure someone who shadowed a pod that they did not know can give you more advice.
Dress professional - if not a suit at least a shirt and tie. (you should dress for the job/profession/role that you wish to achieve)
Be prepared to talk about yourself, why you think you are interested in podiatry and bring up that shadowing a pod will help you make the decision. (she might offer for you to shadow).
Research podiatry on the AACPM, APMA, and the college websites before you go so you know something.
Have an idea of what you hope to get out of shadowing (your goals) and what if anything the DPM should get out of it.
anybody have anything else to add?