My understanding is speech is limited by the development of the palate. The child may well know what she is trying to communicate, in my opinion, she does, but hasn't developed the physical capability to enunciate the sounds correctly. When my boys were this age I could often understand what they were trying to say if I was in the next room. Do you get irritated when people laugh when you're being serious? I remember well learning words, what they mean and how they are used; I'm 58 and still working on it.