Sarah, Izzy was sleeping 8-10 hours from 6 weeks, a bit later than Juliette but still, and then i would demand feed her during the day. She would cluster feed from about 4-7 most nights, almost like she was stocking up for her nice big sleep and I didn't really mind. During the day she would go around 3 hourly or so. As you said, if she is having lots of wet and dirty nappies and seems to be gaining weight I would enjoy the sleep!!!! When she was a bit older, about 10 weeks, I would let her sleep because it was working for us and I would express either before I went to bed so my bb's wouldn't kill, or else I would wake up and do it in the night. I preferred to do it at around 10ish before I went to sleep though just in case I expressed at 3am and she woke up at 4!
Good luck working it out but sounds like your princess has it all worked out!