Meet wife at AA Arrivals Lounge. It's not that hard to find. There are some signs. Or, as others have posted, simply exit LHR customs, curve right, then turn right, look for the lift, go up to Mezzanine level, and the lounge is right there.

If she gets lost, just ask any airport employee where the Arrivals Lounge is. AA Arrivals Lounge is right next to UA Arrivals Lounge, so if you find one you find the other.