She was trying to deceive him.

Perhaps she suspected that he had seen her crying, and now, attired in all a woman's wiles, she was defying him to believe his eyes.
Grizel garbed in wiles! Alack the day! She was shielding the man, and Gemmell could have driven her away roughly to get at him.

But she was also standing over her own pride, lest anyone should see that it had fallen; and do you think that David would have made her budge an inch?
Of course she saw that he had something on his mind.

She knew those puckered eyes so well, and had so often smoothed them for him.
"What is it, David ?" she asked sympathetically.

"I see you have come as a patient to-night." "As one of those patients," he rejoined, "who feel better at mere sight of the doctor." "Fear of the prescription ?" said she.
"Not if you prescribe yourself, Grizel." "David!" she cried.