I think aslong as your DD is well fed during the day and drinking pleanty no dehydration I wouldnt worry too much about her sleeping through for 7hours. Also so long as she is feeding as soon as she wakes I'd be greatful for the nice sleep.
My DS slept from 12am - 6 am last week and I got excited thinkin it could be the start of something cos DS feeds really well. However unfortunately it didnt last lol.
My Mum knows women who have had there babies in a routine and sleeping through the night by 3weeks old so I wouldnt worry overly aslong as she is well fed