You gave her a tirad about communicable diseases and the entire law regarding returning food items to a restaurant and she was sarcastic?
Most McD's does close their grills by 11pm during the week and stay open later on weekends.
So she was right to tell you that the grill was closed (probably was being washed) and she could not make you a new burger.

I am not sure how you usually eat but McD's was NEVER on my diet when I was pregnant. And it is rarely even now. Not the healthiest of foods to be eating while pregnant. Lots of sodium and fats.