Remember that we have two sets of teeth--primary (first set) and secondary (final permanent teeth). Teeth erupt and fall out at varying times from one child to the next. The 20 primary teeth usually come out by two years of age, which are important for function as well as holding a place for the permanent teeth. There are 32 permanent teeth, designed to last a lifetime.
Between the ages of 5 and 12 years of age, your child will have a mixture of primary and secondary teeth. You do not mention which tooth of your daughter's has fallen out, but my bet is it is one of the front ones (usual pattern would be on the bottom). I am also assuming your daughter's tooth fell out on its own, not due to injury or trauma. If not or if there's any doubt, I would have her examined by a pediatric dentist, a specialist trained in the care of children's teeth.