I'm assuming she's tall for her age?
I have a DD who went through puberty early (earlier than your DD such that we ended up being investigated etc). I think I have my facts straight for you.
Growth wise, early puberty means early closure of growth plates and that stops growth. On average girls have done most of their growing before their periods start, and growth will stop within 2yrs of starting periods.
THis meant my DD went to secondary school the tallest and stopped growing at about 5 foot 1. She is 14 and her friends are out growing her. She's fed up with people saying " you'll grow a bit yet" she will not.
You need to be aware/discuss this with your DD. It's been the biggest grr thing for DD2 ( even though she's the same height as DD1 LOL)
Boob wise she will grow a bit more but is unlikely to keep growing to page 3 proportions. We have a devil of a job with bras for DD2 . At 9 she was a B cup and now at 14 is FF/E depending on where we go, with a small back size. However she has been that for 12 months or more.
Bra fitting- is your DD properly fitted at that size? I'd be surprised ( see all the many MN threads!) most 30 A wearers are not that size but a 28 B or something similar! If she's comfy I wouldn't worry though. John Lewis do the best non wired non padded bras up to IIRC a C cup in their teen range. M+S are crap and rude- told DD at 11 that "you are far to young to be wearing a wired bra" , to which I said " well you don't make a DD that isn't wired" ... " oh she can't be that big...... oh she might be..... here we don't do a DD in her back size a bigger back and smaller cup will do" . All over the top of DDs head so we left LOL
DD has been a bravissimo girl since 11. They are so lovely there and the bras fit!
Periods wise DD copes OK. If your DD is very heavy see your GP though. THere are loads of treatments that are easy and help. As long as you have good GP there should be no embarrassing examinations they just are not needed.
HTH the only problem really with early puberty is firstly you "fly solo" with your DD as schools are light years behind. The lillets talk was in year 7 by which time DD (and a lot of her mates!) could have given it blooming thing! Also here the "teen tantrums" seems to have gone on for ever. I think now she's just play acting because she thinks she should, but the hormonal moodiness from a " big toddler" when she was 10 was amazing!
PM me if I can be of more help.