well I have stayed outta this one for the most part - coz I Only use the front brake EXCEPT on dirt. It comes from riding motorcycles where you just don't wanna use the back brake except as a backup (and even then I don't use it). The front brake is the primary and pretty much the only means of stopping so I just translated that to my bicycles. I even have the brakes switched so the front is on the right hand side, where it would be on the Harley.
and yes, when I was riding with Snow I realized the back brake was the better choice for MTBng and had no problems making that switch. V is right - the question is what application is she riding in although I know a lot of ppl that use the back or both on the road. My concern would be: if you're not used to using the front brake - you could go over the handlebars because of the unfamiliarity with the stopping power. I'd rather see someone stick with what they know and are familiar with especially in a clutch situation than try to switch coz someone said they should. Unless it's mashing vs spinning!
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"