This was apparently made in SAI Paint Tool. I especially like the coloration of her hair and dress. The pose is cute too. You can see the full sized version on Pixiv.
また昔みたいに一緒に遊ぼう | ぎやまん＠イナバラ [pixiv] http://www.pixiv.net/member_illust.php?mode=medium&illust_id=22285079
