Definately have a chat to the CHN. They will have seen lots of 3yr olds and 6 mnths does make a big difference.

As a teacher my advice would be to read, read, read and talk. Play dumb to encourage her to explain more clearly. Repeat back to her what she said but using the correct words. Children learn by imitating us. Look at the pictures in books and talk about what they are.

You prob do all of this anyway but I hope it's of some help .