My DD used to sleep long stetches like that when she was around that age. I thought 'Yay, I've got a good sleeper!' Haha - now that didn't last!
Some babies start sleeping through at a really young age, some do when they're little and stop, some never sleep that long a stretch... All perfectly normal.
I'm sure your DD will have (and probably has had by now) a big big feed when she wakes .