Consider the initial consultation to be a fact-finding mission. Chris will visit you and your garden to find out as much as she can about your requirements and wishes. This initial consultation is really a stepping stone to further work. Some of the questions you might want to ask yourself are:
You may know the answer to all or none of these questions, but don't worry, this is the starting point to designing the garden. Also look at the Garden Design section here which lists a number of different garden types. Another question you will want to ask yourself is how much you want to be involved in the garden construction. Do you want to build it all yourself or hire in someone to do all the work? Will you need a maintenance schedule to help you manage aftercare and maintenance?
All the above will help but also remember that if your mind is a blank, part of the role of the consultation is to provide you with ideas of what is achievable and how to proceed.