J.,
Have you ruled out a hearing problem? you might ask to get her hearing tested if you are concerned.
My son just learned 'ba ba' and now EVERYTHING is baba. His sister's name is Bella, he calls her ba ba, tv is ba ba, shoes are ba ba.
I think more important than saying the words correctly is that she is trying to communicate. try to do a LOT of talking to her... tell her in very clear words what things are, and make a HUGE production of praising her if she makes an attempt to say it with at least the starting sound correct. get down to her level and over exaggerate your sounds, get out picture books and say the words of the pictures (i.e., 'truck', 'car', 'shoe', 'puppy', 'kitty', etc.). I am not sure, you don't say in your post, but sometimes if people are doing a lot of talking for them, they really don't have any need for communication... my friend's son at 3 was still walking around grunting and pointing at things... mom was not making him say words to get what he wanted... he would point, grunt, and she translated and gave him what he wanted.
I was concerned that my son still had not said 'mama' at 15 months... and wasn't doing very much in the way of talking...(though he was VERY expressive and communicating in his own way) but his vocabulary has recently exploded and he now says mama, daddy, mmmm good, peeps (peas), nana (banana), papa, cheese, gurr (yogurt), hot, brrrr (like as in cold), thank you, diaper, garbage, and has learned to cover his mouth and nose when he sneezes :)
I don't think you're being overly paranoid, and I don't believe there is necessarily anything 'wrong' with your daughter either. Try to work with her on words, and I bet she'll come around and make up for it with non-stop chatter and you'll look back at this time and hope for it back :)