^ Iroha and Komugi are pretty gay but their relationship just doesn't get artist's fanart juices flowing. Mayu and Yuki have this classic seme x uke thing going, which is arguably "sexier", which means hotter fanart.
Correct, she is canonically bisexual in the books, and in the witcher 3 as well depending on your dialogue choices. Her eyes are also green, not yellow (as she never underwent the witcher mutations like geralt did).