I had congested heart failure, and your mother's coughing can be symptom of CHF and more significantly if there is shortness of breath (hyperventilating especially when inclined as gravity has a role in the degreee of congestion...sitting up helps if not very serious).
The chest edema is a result of poor left ventricle (heart) contractility and the blood from the lungs backs up into the lungs and fluids leak into the pulmonary tissues. The condition can happen very quickly without prior symptoms of ischemia (occluded vessels) etc.
I'm not sure if she has any other swelling. She didn't say and she lives in another state so I don't see her very often. She also doesn't tell me too much. I only found this out because I called her. I hope it's just a bad cold and I hope she calls her doctor. I tried to tell her and she doesn't like being told anything, lol. I'll just have to wait and see.
She's 68 I think. And what's SOB?
They could run together; but, it could be a lot of other issues too. How old is she? Sometimes it takes longer as you get older to beat a cold. You would think that within 3 weeks though a cold virus would be getting better. Does she have any SOB or edema?
It sounds like she should go and get checked out by a doctor and possibly have an x-ray taken to be on the safe side. There is a lot of flu's going around now. I hope she feels better soon.