From watching Cirie's voting confessional, she was in on the plan to blindside Alexis with the idol.

Back during the conversation where Cirie was telling Amanda about voting for her and the purple rock and all that, Cirie offered to tie the vote up but Amanda told her no then we got a cut away from them. I suspect after that, Amanda told her she had or was about to have the immunity idol.

It was evident at TC when Cirie was holding Amanda's hand, then chuckling along with P & A that she was in on it from jump.