I haven't had that happen, but yes it's true some children are genetically missing one or more teeth. Are the gums swollen in the center? Can you "feel" them if you rub her gums? Don't be afraid to take you child to the dentist now if you're worried. I worked for a pediatric dentist for 9 years that specialized in children only. What area do you live in? I might be able to recommend one in your area. In the worst case scenario, if the teeth are not going to come in, you can have a space maintainer (sort of like a child's bridge) put on. This helps cosmetically, it helps with speech development and holding the space so the other teeth stay where they are supposed to. You have to wait until they are about 2, because this appliance has to be cemented to their two year molars. Once it's in, you can't tell. The labs are amazing. They would take an impression of you child's mouth at the dentist office, send it to the lab, then the lab would make two false teeth, that look very real, and very much the same size and shape they would have expected the real teeth to be. These types of appliances are used for kids missing certain teeth and for those kids that lost certain baby teeth in an injury or accident. Again, let me know where you live, some parents would literally drive up to 3 hours to come see the dentist I worked for. If you can feel the teeth up in the gums, or see they are there protruding, she may just be having a terribly hard time getting them through the gums. There is a procedure called a gingavectomy that lances the gums open very quickly to allow the teeth to drop down. It sounds awful, but it is very fast and very effective. That is mostly used for older children getting their permanent teeth in, but you never know, it's worth asking about if it's right in your situation.
Like I said, don't be embarrassed about taking a baby into see the pediatric dentist early. According to the American Academy of Pediatrics, they should go by the time they are 1 anyway. Also, chances are the dentist has "seen it all." We had instances of babies born with teeth coming in as newborns. They had to have those teeth pulled out, so they don't swallow them when they are feeding. Hope this helps, there is ex-coworker of mine on mamasourse boards that still works for him. Her name on here is Linda S, if you see her, she would be very helpful in answering any questions you might have. Just tell her I sent you her way.