Once she studies your hair, its condition, its style, its cut, and your lifestyle (e. g., how much time you plan on spending on your hair each day), she will then make some recommendations for color and maybe even a more suitable style for you. Plan on being there for a few hours.
Have you carefully factored skin tone and eye color into your decision? You really should you know. Nothing worse than walking around looking all washed because you picked the wrong color.