I am an Orthopaedic surgeon and I would be happy to help you today.
By washing surgeon means that the joint would be thoroughly washed with several liters of fluid so as to remove maximum possible bacteria present in the knee joint to bring down the bacterial count.
By debridement surgeon means that he will remove all dead and necrotic tissue as well as any tissue which seems infected in the knee joint.
When bacterial count is brought down it can be tackled with antibiotics. Several weeks of antibiotic use may be needed to control and eradicate infection.
Most of the times regional anaesthesia in form of spinal block is used but the type of anesthesia to be given is the prerogative of anaesthesia doctor. Your fiancee can definitely discuss the type of anesthesia to be used with the doctor and let her doctor know what she prefers.
She may require 3 to 4 different surgeries for eradicating infection as pseudomonas is a hardy bacteria and difficult to eradicate.
Usually the day of surgery is more painful compared to other days. But there are effective methods of pain control and her surgeon can use those methods including intra-articular injections to control pain. He may also consider using multimodal analgesia where several different methods of pain control are used.
Her doctor would be the best person to tell you about walking after surgery as different surgeons follow different rehabilitation protocols post surgery.
Feel free to ask any follow up questions.