Robert Chase had met Annette prior to Harvey being a patient when he was involved with a woman who was into the same lifestyle. He recognized her when he saw her at the hospital, and made discreet inquiries of Foreman about who she was. Foreman thought she was some kind of guru and Chase left it at that.
However, later, Annette was caught choking Harvey. Some of the hospital staff tried to have Annette arrested but Chase intervened because he realized that she and Harvey were engaging in erotic asphyxiation and she had no intent to hurt him and, indeed, Harvey had consented to it. Annette explained that the asphyxiation lowered Harvey's anxiety about being in the hospital. Harvey had been paying her back by cleaning her apartment and doing her taxes. However, she was still banned from the hospital.
However, when Harvey started refusing procedures, they realized they needed Annette back to try to convince him to consent. This backfired when Harvey uncharacteristically pushed back at Annette when she tried to dominate him into consenting.
After Harvey lost consciousness, the team had to find Harvey's parents to get them to consent to the exploratory surgery. However, the surgery found nothing.
Eventually, Harvey's problem was traced to osteomyelitis, and House realized the choking was making it worse. He caught Annette, dressed as a nurse, sneaking into Harvey's room to see how he was. He told her the asphyxiation had to stop.