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!