I know this thread is old, but,, Want to place another recemendation AGAINST a brake. I'd go with light loads and lots of assistance during the first part of her learning period. Yes the brakes help, but the noise is more detrimental than it's worth. Yes she will be wearing protection, but she will still "feel" the blast. We (adults) have been exposed to allot of noise, concussion, face slap, etc. etc. and have been conditioned to ignore most of it by now. Young children can be more sensitive to it that we think.
As for the theory of not noticing the blast while hunting,,,,,we never notice the hearing damage we do when we're doing it, but we do notice what the damage has done to our hearing later. At 8 her hearing is very sensitive. Keep it that way.