My friends Knee has something wrong...?

My friend somehow hurt it knee NO one knows how though it has been getting worse now it is swollen and when she moves it, it pinches also she can barely move it and when shee could the pinching happens. She doesn't want to go to the doctor (and I don't mean doctor who) because she is afraid of the truth.... have any idea what it could be I just want to feel like I am contributing :).