Hi M., I know you have received a great deal of solid advice but I feel compelled to look at the stuttering from a different angle. And for any other poster, please note that this is what I recall in dealing with my son's stuttering and not meant to invalidate your comments.
With that said, my son had a stutter at age 3 that seemed to wax and wane for awhile but then towards 4 years old continued and eventually got worse. Even at three I was worried (like you) and spoke with numerous people - teachers, pediatricians, grandmas etc. They all said don't worry it is developmental. And it most definitely is a stage for most children. The reason I worried was because it didn't let up and my son would often just not speak out of fear.
I took him to a very established speech pathologist who diagnosed him with dysfluency. Before I get you upset, I only want to point out what to look for in terms of the symptoms of "problem" stuttering. We were told that if he/she stutters at the beginning of a word that is more in line with development. But if the stuttering is in the beginning, middle and/or end, you need to get it checked out. Also my son had very pronounced hand signals and arm waving when trying to talk. This is called a secondary gesture and that enabled the Speech Pathologist and Pediatrician to diagnosis him with the more adult form of stuttering and with that we were able to get him into an early intervention through the school.
Since you sound so worried I just wanted to give you clear signals to look for - not to scare you. My son, with about a year of therapy, actually learned to internally slow his speech down and by the time he hit 7 had not even a hint of stuttering. He was taught to say to himself (even out loud) "slow easy speech Jack". This acted like a positive trigger which switched his mind to a more calm state. It was amazing to watch.
I wouldn't worry at this point at all; my intent is only to give you more info and hope if the stuttering continues and you become even more worried.
You sound like a wonderfully attentive mommy. You daughter is very lucky.
All the best - H.