As far as I know radon doesn’t exist where I live thankfully. I have dealt with methane before, could you put a small fan in the basement to exhaust any accumulation to the outside to help with the sealant you’ve put in? I don’t know how radon acts as far as gravity is concerned but is it heavier or lighter than air and place the suction of a fan in the needed elevation. I hope she recovers quickly and completely!!!!
