Tours from the airport

Hello all,

My mom will have an 8 hour layover (7a to 3p) in Johannesberg at JNB airport and I was wondering if there are any cheap/free tours she can take during that time from the airport and back. It could just be a bus or something.

This is all part of a long trip for her Chicago to Sao Paulo (to see me) then from Sao Paulo to Lagos, Nigeria (where the JNB layover will happen) then Lagos back to Chicago. During the last leg of the trip she will take Turkish airways which has a complementary Istanbul tour so that will help with that 13 hour layover. In all almost 60 hours of travel in a two week span.

For background she has never traveled on her own before so worried about what she will do with the layover. I would rather her not waste the 8 hours in a new country at the airport, but also want her to be safe.

Also are there showers she can use at the airport?