No offense to her, but was it truly swelling (ie a circumferential difference from left versus right) or just a fatty deposit? I have treated many women of that size who just have odd lumps of fat around the knees ...
She could also have a pes anserinus bursitus ... it's sort of where the hamstring and adductors meet on the medial tibial plateau ...
In that case, she will benefit from some treatment by a PT ...
here's an article on pes bursitis that is good ...