Agree with PP. Is she formula or breastfed? Formula fed babies may not eat as often as breastfed babies. Great news that she's sleeping well! Growing baby!
Like pp have said, as long as your LO is gaining weight and wetting enough diapers, and eating well during the day, you can let her sleep as long as she wants. Every parenting website and resource uses a different variation of timing, but most recommend somewhere between 4-6 hours between feedings at night. Formula fed babies can probably go longer. But, as long as she hasn't had problems, she will wake up to let you know if she is hungry!
Re: Eating
Baby #1