The cheapest brake will be any brake for a 7.62x39, probably an AK-74 type. The recoil will not be signifigantly reduced because the AK round is a low pressure round, compared to your 54R round, which is high pressure. An EFFECTIVE brake will be one made for the .308 round, however these brakes tend to be much more expensive. Either way the only RIGHT way to do it would be to have the muzzle properly threaded, and that usually means a gunsmith. The easiest way around this, of course, is to tell her she needs to tough it out and get used to it. I have a mosin scout that I cut down to an 18 inch barrel. I have a Pachmyr "decellerator" pad on it, and recoil is really not that bad. My wife took it with no more than a shrug of the shoulders. I also understand that everyone is different. Good luck with whatever you choose to do.
