Re: Training Bra?
I would imagin this is more of a parenting issue. If you want to let her rush into womanhood well before she's ready, just because she's pressuring you to let her, that's your decision. But you're going to have a lot of decisions like that, e.g. when to start letting her wear makeup, 'mature' clothes...
Personally, I feel a girl should wear a training bra as soon as she begins to develop breasts, any earlier is not necessary. The point of training bra is not only to get you used to it, but to get a girl past that awkward stage of small breasts that really don't need any support. If she is a slow starter, and is feeling 'behind' her friends, who already have breasts, then I would let her wear one then. But not before her peers have breasts (and if they're all wearing training bra's w/o any need to, then it's something you could talk to her friend's mother's about). If they're all 9 and wanting to be 'sexy' like Brittany Spears, I wouldn't encourage it. But that's just my opinion.