Hello,
I cannot confirm anything without examination but it can be dermatitis or allergic reaction. Ask your mother to take some antihistaminic like Benadryl( may cause drowsiness) or Claritin and apply some calamine lotion and mild steroid cream on the rash. If the symptoms are severe then oral steroids may be needed. Also if it starts growing or becomes annular, then the possibility of granuloma annulare has to be ruled out.
I hope it helps. Take care and please do keep us posted on how you are doing. Kind regards.
My mother has a red bump looks like a small red dot in her finger and doesn't hurt or itch. Im worry. What is it?