Free: Contests & Raffles.
A 30-06 won't kick bad at all in a BAR. But I agree with carpsniper- the 270 will do just as well. The main thing I'd be concerned about with a BAR is the weight. Are you sure she is able to pack a heavy rifle like that all day?
You can look into the BOSS muzzle brake that Browning designed and includes (optional) for the BAR, if you are concerned that 'too much' about the .300 Win Mag is regarding recoil. The standard cartridges also give one extra round for the standard set-up.