Your mom seems to have lichen simplex chronicus
It is a type of eczema
, in which the lesions are tough,dry,blackish and itchy.
Psychological stress can exacerbate the lesions.
Tell her to avoid soap bath.
Antihistaminics may be continued for long time.
Excessive rubbing and scratching increases black color.
The color may fade after few months.
However, you consult dermatologist
I hoe you got my answer.
Dr. Ilyas Patel MD