添削結果を受け取りました。いつものことながら正しい英文を書くのは難しいことを実感しますがその内添削箇所ゼロとなるように努力したいと思います。

The great lady said to Maggie, “Remember that when the Duchess arrives you must say ‘Your Grace.”
Maggie had recently been employed as a maid at the great lady’s house through her distant uncle. The Duchess was coming as a guest that day. Maggie was determined not to make any mistakes on this important occasion so as not to make her distant uncle lose face.
The moment arrived. The carriage of the Duchess stopped in front of the house. Maggie opened the door of the house to greet the Duchess. But by what happened next, the Duchess and the great lady as well as others around were stunned. Maggie, of all things, intoned aloud, ”May the Lord make us truly thankful for what we are about to receive.”
Maggie was born and raised in the village and didn’t know anything about the customs of the aristocracy. When she heard the great lady say, “Say Your Grace,” how could she have known that she was being told to politely address the Duchess by saying “Your Grace”? She only tried to do her best to fulfill what the great lady had told her to do but she had made a grave mistake. To her, “saying grace” meant saying a prayer of gratitude for the food to be received at meal time. Her parents had instilled this practice in their household since she was a child. Therefore, instead of a polite greeting, she said a meal-time prayer to the face of the Duchess. This mistake must have horrified everyone.