About time we saw something new with Kaoruko. She need not worry about her looking different and less prepared than usual. I'm sure everybody appreciated seeing her like that, Rintaro himself included. I'm also sure she felt inspired to do her best after overcoming the initial embarrassment of unexpectedly getting seen at work by her boyfriend.
"But still... I really love him"
Look at her earnestly coming to her now boyfriend's defense, trying to point out his best points. A precious, tender look on her face, the face of a good girl deeply in love with an equally good boy. Good thing Miyoko was a bit more understanding and not super closed minded, after imagining "delinquent" when she was first describing Rintaro. The old woman was willing to hear more instead of instantly dismissing him and telling her to stay away just because of his looks.