9 is normal. Puberty is normal. This is not precocious puberty--and breast buds typically seem to develop overnight!
I think it's okay to be gentle with yourself as you freak out, but--try to get through that quickly so you can be strong, supportive, and positive for your daughter. If you've not yet talked about puberty changes, it's time to start! There are a lot of great books (esp. The Care and Keeping of You) out there that DD will enjoy. if this is happening just now at 9, she's not the first in her class, even, that's started developing breasts (and no, the girls who did so earlier are not necessary fat, soymilk-swilling girls who drink out of plastic bottles all the time).
I freaked out a for a bit when my 8 year old started developing (you could probably find my freak out post here). :) But you know, seeing her interest and low-key excitement about the changes got me excited as well. I'm so proud of her. Her strong, healthy body is developing beautifully, and (so far, with some heavy duty work on my part to countermand the really horrible and sad messages about girls' puberty that are vomited everywhere these days) she is confident about her growing and changing body. to me, that's my duty now.