When I was worried about my oldest son's verbal development (he talked sort of late), my pediatrician said to play a game with him to see if he was capable of learning new words. He said to hold an object you know she wants, just out of her reach, and say the word. Then say it again. And again. Say it over and over again until she says it back or shows the teeniest sign of getting frustrated. Really, that's probably only 3 times :) Make sure you treat it as a game and keep it fun.
The point, he said, was to see if, in a week, my son had learned a new word or two. If so, then he was fine and just preferred not to talk. If not, then we would talk at our next visit. (this was his 18 month visit, so he wasn't worried until his 24 month visit).
Another thing he mentioned is that animal sounds count as words. So when my son would see a cow and say "mooo!" that counted toward his vocabulary. When I heard that, I really stopped worrying much, because he knew all sorts of animals.
Also, my nephew refused to walk and talk for the longest time! I think he was 17 months before he walked, one month before they were going to start serious developmental evaluations. The stinker just knew life was good being carried around :)
As for talking, he just had no interest, it seemed. Then all of a sudden he said a sentence. His first word was a sentence! He never said, "gimme," he said, "Can I have that please?"
My point is that kids develop differently and your duaghter is probably fine. But I know how I worried about my oldest! I was a lot less uptight about my second, and now I have a 14 month old who could care less about talking. He will say Mama about 1/8 of the time if I ask him. I know he understands me, though, because he will go get something if I ask him to. That's the most important part.