How To Get Rid Of Itching Below The Knees?

my sister is 57, lives in a hot country, is on her feet walking and running and lifting all day in a warehouse, and has recently been experiencing maddening itching below the knees. Her blood pressure was way too high, at a doctor's visit today, and he's asked her to come back in 3 weeks to see if it has gone down. he's prescribed some medication and a water pill. Could you provide any quick answers to the likely cause of this itching? Thank you