Ok. Then I was mostly right. The knee capsule is to the knee what the "rotator cuff" is to the shoulder, in that there is no such thing; it is a collection of structures that the doctors point at and say "It's in there, somewhere". A sprain like this is basically saying "She hurt her knee, but nothing serious or specific", which is pretty much happens when you jamb a knee, or a wrist, or some such.
Glad to hear it. Positive waves.