Hello!

A friend of mine was supposed to fly ARN-ORD-RDU on AA, and was rebooked on BA ARN-LHR-LGW-RDU(AA to RDU) with three hours to connect between LHR and LGW. Her flight arrives at LHR on a weekday morning in May, and her departing flight leaves LGW at noon. Is this enough time? I checked the BA website, and it shows the minimum connecting time as 4 hours. In reality, how long will this connection take?

Thanks!
Ilves