The purplish "scar" you describe is what gets left over after any inflammation on the legs. It takes many months to go away and requires no treatment. As to the other rash, which I cannot relate to the spider bite, you need to see a doctor in person. This may be a bacterial infection. If so, antibiotics may be required. In any case, you need proper diagnosis, which may involve cultures or other tests. This will take a visit to a live doctor.
Best.
Dr. Rockoff