Flaring hip?
 

I have a fit question for you. Today while we were riding, and I have noticed this before, Kathy's left knee "flares out" at the top of her pedal stroke. The right side stays inline. Her hips are not rocking. Any thoughts???

Left shoe SPD / cleat aligned outward? Might be that it becomes very apparent at the top of the pedal stroke.

I notice asymmetrical postures or movements because I have a similar problem. I believe it stems from years of a painful back problem, which is no longer much of a problem, but seems to have caused permanent list. I also have a knee that tends to flop to the inside and brushes the top tube. I mostly corrected this with a shim under the right cleat and padding under the arch to push the knee to the outside.

There may be an old injury that caused some muscle memory like the dog who injured a leg requiring walking on three legs for a while but still walks that way long after the injury has healed.

I see many people doing that, some of them folks who regularly ride very long distances. I'd wonder, does she need to do that for some skeletal or old injury issue? Would it be a good idea to try to modify her stroke or not? I wouldn't do anything without thoroughly discussing it with her.

Is there a leg length discrepancy? A leg flaring out could mean the saddle is too low. If it's only with one leg, it may be "too low" for that leg only (meaning the other leg is shorter).

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.