With DD1 (3.31kg at birth) I was told I could stop waking her for feeds at night once she regained her birthweight (about 2 weeks). With DD2 (1.84kg at birth) I was told I could stop waking her for feeds at night once she was 3kg (about 6-7 weeks). I always ensured I fit at least 8BFs in during 24 hours until they were a few months old though (so just fed more during the day). Both of mine have been great night sleepers from an early age. In my experience, I would say its ok to let her sleep at night (so long as she's regained birthweight), but perhaps make sure she's at least having 8BFs in 24 hours to ensure your supply builds enough - she will be wanting much bigger feeds soon!