Does she have any wedges under her cleat, or in her left shoe? I recently had some similar right knee issues sorted out by an experienced fitter. Turns out my right forefoot is canted about 15° relative to my ankle, while my left is neutral. Without wedges to cant my right forefoot, my knee would come in on the downstroke, and swing out on the upstroke. The other possible problem that came up in my research, is lack of hip flexibility. If she doesn't have adequate flexibility at the top of the stroke, she may swing the leg out to give the hip a bit more room. Taller or closer bars to raise the torso a bit, or possibly shorter cranks would help in the short term, but stretching / strengthening work would probably be the best fix.