^I got the impression she was more out to show up Nemo one way or another since she was clearly peeved throughout over having sucked at table tennis (and Nemo sort of having rubbed salt into the wound). So when one hour of, ahem, special training failed to produce Dramatic Shounen Manga Powerups she Plan B'd to getting all smug over spending the evening with Tomoko instead. (Nemo's reaction looked mostly like "errr... am I supposed to retort to something so mundane...")
Probably the most we've seen Yuri actually smile in a single chapter mind, even if it was a delightfully smug little triumphant smirk much of the time. Hanging out with Tomoko & Co. is definitely having a positive effect on her. (Cue my earlier thesis about Yuri being one of the characters who reflects and parallels different aspects of Tomoko and her growth as a person.)