I thought it might be Mio since the shirt looks the same (the blue bow at the top) and the haircut looks somewhat similar. In the show, there's also a time where Yui says 「アイス食べたい」. There are some videos with her begging for ice cream http://www.youtube.com/watch?v=adVwVZIMgLE However, the artist confirmed in a comment that it was not Mio.