Read and understood your history about your Mom and understood the problems. The hives which develop after a week of having cough ans cold can be due to urticaria as and you know, anything under the sun including the sun can cause allergic reactions.
Hence the first part of the management is to list up the things which could have caused this: the list includes the things she ate, drank, the dust, molds, mildews, pets, scents, and the list is endless.
By listing it becomes easy to find out the factors and avoiding then is a part of the treatment.
I would give her a dose of an antihistamine and steroids.
Investigations of the blood, urine, stool, X-ray chest are mandatory and the treatment of the primary problem of the cold and coughing has also to be done.
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