Isn't it strange that people can say it isn't NORMAL. We're all unique so nothing is NORMAL just it can be rare etc. Cancer isn't NORMAL but look at all the people who have it and all those people with rare diseases. Are we going to say that people who can't have children aren't NORMAL, how pathetic. If your sister does start puberty early it isn't because she isn't NORMAL it's just that it's not very usual at that age.
I know of a girl who started her periods at 9, and there was nothing to show she wasn't NORMAL.
As others have stated, make sure she showers daily and she'll be fine.
I can't understand a doctor using the word NORMAL ... he/she needs to change his /her choice of vocabulary!