As a high school teacher, Mikkayla would be super-aware of the destructive nature of peer pressure and bullying tactics, yet she led the charge against Justynn in an appalling display of systematic bullying. All of them (except Tahan) treated Justynn horribly because they felt they had permission to do so without repercussions, because he was universally disliked. It was like the Lord of the Flies in there, and Mikkayla was the worst culprit. His treatment was very revealing about the HMs true natures and sense of ethics, also showing Tim to be way more conventional than he likes to think himself and weak under peer pressure.
But back to Mikkayla...I see her now as the house's alpha. Most of the others are intimidated by her forceful personality. Tahan is the underdog, and Mikkayla takes every opportunity available to try to undermine her to the other HMs so that no one likes or respects her. That is classic bullying.
Another reason I dislike Mikkayla is she's always so free with her opinion, never happy to just give it, but to try and force it down people's throats, but time and again she's shown her ignorance. Also, she votes Liberal, which isn't surprising actually, but as someone who cares about social justice, I find her politics repellent.
I feel bad for her body issues, but I think, once again because she's a teacher of teenage girls who have issues with self-esteem, that she's setting a really bad example and being totally irresponsible by publicly saying how she "hates" being Asian and "fat". And she thinks she's some kind of role model??
Of all the housemates i think she has the most aggressive focus on winning the game, as seen by her sour face when Ben came back and when the male intruders arrived (I didn't notice her reaction last night because the show was boring I was engrossed in a game of Candy Crush). My mind boggles at why she thinks she, above everyone else, will win the game, considering she's utterly charmless, not in the least entertaining, and the least likeable person in the house. She's also been totally shit at training that dog.