In “Scandal in Belgravia”, when Sherlock and Mycroft strolled into the morgue to see Irene Adler’s body and found Molly Hooper there, Sherlock seemed genuinely surprised (even if it doesn’t show on his face) that Molly was in for that night to assist them with Irene’s body. Even after the horrible things Sherlock said to Molly at the Christmas party.
And I think Mycroft personally asked Molly to assist them because he wanted to protect his brother’s dignity. Mycroft knew that Sherlock was somewhat attached to Irene Adler and any emotion (if there is such that will come out of Sherlock) will be a show of weakness. Mycroft asked Molly because he’s aware that she’s part of Sherlock’s “Team of Carers”, like John and Mrs. Hudson. And bringing in another pathologist will just not do.
And of course Molly would say yes. She could have been reluctant at first, (because, hey, who would want to work on Christmas Eve?) but because it‘s for Sherlock, she did so.
And when Sherlock said that she didn’t had to be there, Molly said that it’s okay and explained that everybody else were busy with … Christmas.
And the way Sherlock looked at her at that scene seemed like he’s beginning to realize how important Molly was to him and to his work. That Molly would do anything for him, even postpone her own Christmas plans (if she had any) for him.
And Molly’s care for Sherlock was greater rectified in “The Reichenbach Fall”