She's turned on Jack in particular, because her, Danny, Christian and Jack had a pact from the start, something about sharing the money whoever won. Chloe thinks that either she or Danny will win, she did think that Jack would for some time, but since his boos she has slowly turned against him.
Jack has proclaimed that he is now out for himself, and I think probably because Chloe turned on him even before this money arrived. During the hotel task, when all Chloe had to do was sit and be waited on (and suck up to Helen) she launched at Jack for eating a pastry when he hadn't, she assumed he had straight away and I think that showed Jack that as far as trusting each other, it is a one way street. Jack then bit the pastry and I don't blame him. It wasn't Joel going at him that made him do that, it was Chloe shouting at him straight away, assuming he had.
I don't blame her for wanting the money, most, if not all of them, do, but to constantly try and discredit Jack is simply her trying to make him look bad so he leaves on Friday. Harry is doing much the same, both trying to make someone more of a target than themselves.
Hopefully either Chloe or Harry will leave, preferably both.