Ms. Seward believes that Meghan Markle simply couldn't bear the thought of being in a country where "people don't like her." In her opinion, Meghan's reluctance to attend the Coronation was mainly due to her discomfort with the idea of being surrounded by people who don't have a favorable view of her.
Ms. Seward went on to suggest that Meghan could have still attended the event with her husband and shown up looking stunning, despite any negative opinions about her. However, she believes that Meghan lacked the courage to face the possibility of being in an Abbey filled with people who dislike her, and perhaps even a whole country of people who feel that way.
In summary, Meghan Markle's reported aversion to being in places where she isn't well-liked may have played a major role in her decision to decline the invitation to the Coronation.