I noticed this with my 4 year old when my nephew turned one last year. He not only turned his speech but his bahavior reverted...it was quite annoying as I am partially deaf and really could not understand anything he would say!
He only sees them a couple times a month, but this taslking and bahavior lasted for weeks. Actually, when we see him, my son will still do it!
Now that he is in pre-school, he turns into all kinds of other kids. I guess this must be normal, my doctor said he is fine.
The pre-school instructor says she did a little test with him and his pronunciations and he is fine. They all say not to worry.
We live in MI, and my daughter was called 'our little New Yorker' for her speaking. She just did not say the r's. She finally enunciates properly at 8, but I was worried and asked teachers and speech therapists so many times. They all said she was fine, and now I know she is! ( guess it was behavioral, since she would say all words correctly when I worked one on one with her.)
I guess I am trying to say, your daughter is most likely going to be just fine and grow through this phase! Try to relax!
I did make games to play with them - they had to identify, and say specific words in my concentration-like game. Then I knew they were ok. They could not find the next rabbit or llama unless they said it loud and clear...
Sorry, that got long!