The letters "RD" after ones name signify that she has completed at least a 4-year college degree in dietetics.
After graduating, she must then complete a minimum 900-hour internship which trains her in every area of dietetics and nutrition practice. A national qualifying examination must be passed after completion of the internship to attain the "RD." In order to maintain certification and licensing, she must complete ongoing continuing education.
All Registered Dietitians are technically "nutritionists", but not all nutritionists are dietitians. A "nutritionist" typically acquires certification through an online program and has varying standards and practices from a registered dietitian.