Dear [Ms. Interviewer's name]:
[Name of person referring you] at [where ever you know the person from] suggested I contact you to ask for advice about pursuing a career [whatever area you are pursuing]. I worked with [name of person referring you] last year as part of an internship and found the work to be extremely interesting. [Name of person referring you] suggested that an excellent first step in my career search would be to speak with you.
I am going to be in your area early next week and I will call your office then to see if I can schedule an appointment with you during that time.