Eighteen years is a long time to commit to anything. For Kathy Rinaldi, it was 18 years as the face of American women’s tennis, someone who could always be relied on: at the juniors, at the majors, at the Olympics, and in between. On Wednesday, the former WTA Pro announced that she was stepping down from her position as USTA Head of Women’s Tennis after nearly two decades, and tributes poured in from senior players, including Chris Evert and Dan…