I agree with all replies. If you have no previous experience with counselling or understanding of secondary gain behaviours, a psych referral for the patient is needed. You could try to find out what her fears are regarding the knee pathology. Was the patient on antidepressants before the knee injury?
I recently had a patient with a knee injury from high level combat sport, and both the surgeon and I felt that cruciate, meniscal, and collateral ligament damage had occurred. The patient did not respond to the usual physio, or even 'unusual' physio. A subsequent Wikipedia reference-linkMRI was normal. Management chosen was conservative, with rest, knee brace, then strengthening physio. The case of the severe pain and loss of movement may be due to a combination of bruising, oedema, and meniscal irritation, plus muscle guarding effects.
After rest, the patient is doing well, and expects to restartv training for competion later next month.
If skin discolouration , abnormal hot/cold/ hypersensitivity etc is occurring, consider CRPS (chronic regional pain syndrome).
If this is confirmed, she will need emotional support, and time, as there is no reliably consistent treatment.
Good luck
MrPhysio