Dont give her crap for being 3 months under 13, big deal. She needs help, this is a good place to get it.
I didnt get noticeable breasts until 7th grade, but mine started growing in 5th grade. I reached a C cup in 7th grade, I think I was early. But, most girls dont get larger breasts until atleast 8th grade. Its fine if they arent big, no need to worry. You'll be in puberty till you turn like 18, you've got plenty of time.
I got my period in the 6th grade, most of my friends got it around that time as well. What Ive heard is that you dont get your period until a year or so after your breasts start developing, and I never had any of that discharge stuff until a year after I started my period. I get it too, like every day, but it doesnt smell and it's clear. I just use a light days liner for that problem. Id always heard that if it smells or is any other color than clear, that you need to see a doctor, could be a yeast infection or something similar - get it checked out.
Also about the hair, I got underarm hair in the 6th grade, and pubic hair maybe in the 7th? But my hair grows very fast, I shave every day
Hope that helped some, if you have questions or need to talk, send a PM or an IM.