He wasn't mistaken about her personality; she was usually soured and abrasive, but she truly only behaved that way in response to others. Most people bothered her for one reason or another - or sometimes no reason at all - but if you were lucky enough to get away without testing her patience, a sweet lovely Lily was all you were left with. Zach was one of the lucky few who got to see it.
"Oh!" Lily cried in surprise as he picked her up and spun her around. Well he was awfully happy about this, she thought happily. She wondered curiously if he had been interested before and had been plotting this. It seemed unlikely, but why else would he be so happy? But that wasn't to say she didn't like being spun around, and when he finally set her down she was a bit dizzy, but all together happy and smiling.
She curtsied playfully, smiling at him. She was tempted to tease him, but she didn't want to ruin whatever it was they had going. After all, it would've been a shame to scare him off before he even got to know her properly! But then he quickly obliged to carry her back to the castle, and before she knew it, she was off her feet again - it seemed to be a reoccurring theme.
She smiled as he turned to look at her, and she thanked him quietly. When he turned back to look where they were going, Lily buried her cold nose in the crook between his shoulder and his neck, keeping her face warm on the trudge back to the castle. Oh, and then she got to smell him as well, but that was just a plus. She tried to keep from strangling him with her arms around his neck, and since he had such a good hold on her she only clutched her hands together, one holding her hat.
Lily was rather disappointed to end her evening with him so soon, but it would've been a lie to say she wasn't looking forward to the goodbye. And anyway, they were going to meet up again for Hogsmeade, so that was a plus, even if it did seem like that weekened was awfully far away. She looked up occasionally to see where they were at, and she clung to him as Hogwarts got closer and closer; she didn't want to get down.