Two things really.
1. If it's a "message for Ben" why is she saying it behind his back in the Diary Room?
2. If "being horrible" is a just cause to not like someone, then Shabby herself should be universally hated.
She just humiliated Ben by pretending to be nice to him, and finally make an effort to like him and treat him with the same level of respect as she does for the other housemates, but then reveal to Caoimhe that it was just a task and then laugh about it. Now, THAT is being horrible.
Just my opinion..
EDIT: Changed the word "hate" to "not like" for absolute accuracy.