Why does Grace lie about where her husband at the meeting? Where exactly is he?

Grace doesn't want anyone to know that her husband chose to fo to a football game rather then the reading of the will. For her, it's all about appearances.

“Dr. Wexler was called away on an emergency operation.”
“An emergency Packers game in Green Bay,” Turtle confided to Flora Baumbach, who scrunched up her shoulders and tittered behind a plump hand.