Hey, it depends really on what your friend would like to get out of her flight. ATL-MAN isn't the longest haul, roughly 6:30-7 hours depending. It's a pretty popular route so she might find that she benefits from either an exit row or extra leg room seat. I believe she can book both online for £35/$50 each way. There's a few other bits and pieces that she can use - they are explained on
this page 
Hope this helps!