Some children are just slower (or not as interested in some things) than others. Remember, mile stones are just BASIC ideas about when your child should be able to do certain things. It's not the same for every child. And, at the stage that your son is, there is no telling if she would start walking next month or in 2 days. Its simply when she decides to. At least she is supporting her weight on her legs, so it isn't like she will have any complications due to her not walking by herself. Maybe try getting her to walk only holding ONE hand. That may get her closer to doing it on her own.