Numerous times, just constantly. Even today the clip showed up of Zoe saying "can't wait for you to be evicted, bitch" then lied to her face about it. Then the other clip that came up of Zoe loudly calling Estelle desperate when she was talking to Michael, tell her she craves male attention all the time, they are just a few at the top of my head. It's not physical bullying obviously because the cameras are on, but if they were stuck on an island and not in the BB brother house, I'm sure it would have escalated to physical violence.
Can you imagine how it'd feel being stuck in a house with no fmaiky or friends, can't even contact the outside world, can't even go online or watch tv to try to take your mind off it. Your forced to interact with a bunch of people as your only entertainment, and those people all ignore you, talk over you, insult you, talk behind your back, etc. It'd be hell, Estelle is strong as f+ck for putting up with it.. I doubt many of us could have. They only pick on her because she won't fight back, she's an easy target. They are vultures, and I was an Estelle hater when I first started watching myself, because sadly we believe what we hear at first, and all I heard was how bad she was by all the others, but as more footage was shown, it's now quite clearly the opposite.