dogs lose their last baby teeth (usually the canines are last) at 6 months, so that is not a possibility. unless of course she didnt lose some of them like she was supposed to and it finally got loosened up somehow.. its common in small dogs to have their baby teeth impacted and need to be removed under sedative/anestesia. she should only have 6 teeth between her canines on top and bottom, if she now only has 5 then she lost a tooth and it wont be coming back. not a big deal, it happens sometimes! if youre concerned you should have your vet take a look, s/he can tell you whats going on.