I also agree to not stress just yet. I think the others have offered very good advice. I just wanted to add that informing your daughters doctor about your concerns would be a great step. I have an 11 year old boy and a 3 year old girl. My son is autistic however, my daughter is not. One of the red flags for his doctors was that he was speech delayed. However, he had other issues too, for example, he had an odd sleep pattern. He slept for 2 hours out of every 36 hours. He would not sleep anywhere except in his car seat. He did not recognize his name until he was 3. He did not laugh until he was 10 months old - I can still remember the first time I heard him laugh!
At any rate, delayed speaking can mean various things or nothing at all. A doctor's evaluation is really good advice. :) I have a friend who has a child that is selectively mute. He can talk, and does at home but refuses to talk anywhere else. I have another friend whose fourth child wasn't talking like she thought he should be and turns out he had fluid behind his ear that was causing him to hear like he was under water. They were able to determine this by taking him to an ENT and the ENT's office conducted a air pressure test - I guess that is what you call it. She said they put air pressure in his ear and was able to see how his ear drum reacted to it. Anyway, he had ear tubes, went to 3 months of speech therapy and you would never know the child had any speech delay now. :)
So, I mean, I really don't think it is anything you haven't done - trust your momma instinct! If you are concerned, ask the doctor and at least bring yourself some peace of mind. :)
I hope you will keep us posted on how things turn out.
Best Wishes
Jen