F*** them. It's her body, she can do with it what she wants, especially if it's causing her pain. (Call me a comfort hog, but why experience pain when you don't have to?)
It's the same response a guy can expect from me if he suggested I get breast implants.

Because I'd be foolish to turn down bigger breasts and get favorable attention from men? Please.
(Sorry, it's just the suggestion that women should aim for what pleases men really gets my feminist goat...

)
And it's not just the back - constant bra-wearing causes shoulder pain as well. Heck, it's the main reason why I stopped wearing a bra in the first place - the shoulder straps were too damn annoying, and I have nothing to support! I'm

thinking of what kind of shoulder pain I'd have if my bra had to hold up 5-pounders!