What Is The Itchy Red Rash On The Legs Along With Dizziness?

My mom has a very dark red rash that is solid from her ankles and up her shin on both legs. It is unbearably itchy at all times. She has also been experiencing a lot of dizziness along with it. She is 67 years old and takes blood pressure meds. but her Dr. says that it isn't caused by the medication she takes.