Estelle has three types of fans:
1. Those that genuinely like her personality (which is odd and not for most, just like in the BB house).
2. Those that think she deserves to win as she's the least bitchy in the house (which is valid if you like nice people even if they are uninteresting).
2. Those that just want to piss off the popular group (I call it the "fuck you popular group" vote).
The first and second groups won't grow much more, but it's the last that has the potential to explode if the others keep targeting her with their bitching.
The more they bitch and Michael says things like "Estelle can't win this" and "I don't understand how could she still be here", the more people will vote to save her specifically. Zoe and Sam weren't getting this "fuck you" vote as their not the main targets and if you don't like them you don't care whether they stay or go (plus they have been bitching a bit too.) Angie was way too much of a mega angry bitch to be saved and she just got back what she gave, you know karma's a bitch. Layla's vote is all popularity.
I'm in the last group, I don't like Estelle as a person but she's received 90 percent of my votes. I only voted for others a few times as a means of voting against Angie who I can't stand. If this hadn't happened to piss me off, I'd have gone the whole season without voting.