At 6 months baby is more than physically capable of dealing with flight. There really is nothing you can do about hearing protection, as there's probably not a 6-month old ever lived that would leave a headset of any kind on
Many car seats will not fit rear-facing in GA airplanes, go ahead and let her sit forward facing, AS LONG as the car seat is a convertable carseat that is MEANT to face forwards as well as backwards! Under no circumstances use an infant car seat forward facing that is ONLY designed to be rear facing.