Those who know Maud say she is emotionless. No, that's quite far from the truth, actually. No, Maud wasn't emotionless. Expressionless, more-like. Though, even then, she did smile once and again for two very special people in her life.
Much to Boulder's chagrin, her exclusive smiles were for the boy and her sister.
When the boy came over for Thanksgiving, meeting the Pie family for the first time startles just about anyone. The boy, however, stuck it through. He dealt with Maud's younger sister's literal punches; he tried to start several conversations with the other sister—more punches came, for that one; he'd even suggested to Pinkie that she should attend Canterlot High when she's able. This, of course, earned him another punch on the shoulder.
And throughout the entire dinner, Maud was smiling at him.
Boulder was seething with unadulterated rage, but as he is a rock, he was not actually seething. Cool to the touch, actually.