This statement suggests that someone who leaves a lasting impression of positivity and happiness is likely to be remembered by others.She who leaves a trail of glitter is never forgotten" implies that a person who spreads joy, positivity, and beauty wherever they go will leave a lasting impact on those they encounter.
The phrase uses "glitter" metaphorically to represent the positive and memorable qualities that this person possesses The quote celebrates the idea of leaving a positive and memorable mark on the lives of others.