Hun, it sounds like you are your little one are doing a fantastic job. 8 hours is a long time for a baby of that age to sleep, but as Jas has said, it does sound like she is getting enough and doing very well. You have possibly heard that night feeds are the ones that do the most for maintaing your supply which is why you are concerned. It is true that the feeds between about midnight and 5 am are the ones that raise your hormone levels the most, and so can affect supply the most. However, the most important thing for supply is frequent feeding, and 12 feeds in 24 hours certainly does that.

The one thing you might find if your DD keeps sleeping so long at night, is that the contraceptive of bfing might be lessened by not feeding during those hours of 12am - 5 am. If falling pg again quickly is not in your plan, this is important to know so that you can make other arrangements.