I'd say she wasn't so much mean, at the onset, but rather intolerant & dismissive, & that's what stuck in people's craw. That ignorance was meant to wane, as she grew to know him, & it did. They're in a very different space by season's endThere is a very wide perception that "Pulaski was mean to Data". I don't agree with it. She was confused by him, adapted and showed him a lot of warmth. But reputations stick.
Her issues with Picard however, seemed to still be lingering. Albeit, he has an equal part in that. Her warming up to people like Worf did a lot to counter that though, imho