Originally Posted by Blumie

The fast track pass that AA will give her is worthless if she stays airside (although I agree that's what she ought to do). After taking the flight transfers bus from T3 to T5, she can use the fast track lane (on the far right) at T5 security if she is flying J on her connection to MAD. Access to that lane is determined solely by class of travel as shown on the boarding pass, not by having a separate paper pass.

After clearing security, advise your wife to turn left, walk to and descend the escalator, and at the bottom of the escalator make a u-turn and double back to the escalators that will take her back up to the BA south lounge.