Think hard about WHEN she does this. Is it mostly when she is excited and trying to express herself through a lot of excitement and energy? Or conversely, does she do it when she's really tired out, or needs something to eat, or is distracted? Or maybe both kinds of situations are when she does this?
It's very normal for kids around this age -- yes, even kids who have been excellent talkers -- to prolong sounds and stutter and repeat words and phrases as if they can't get things out. Some kids do things like this: "And I, and I, and I, and I petted his doggy!" or "It's, it's, it's, it's daddy!" She may be doing this as well.
Yes, it's worth talking to the pediatrician and also worth getting some good parenting books that talk about ages and stages. Those books will discuss kids' communication skills at specific ages. Because she is learning a lot of new words almost daily, and because she is opening up rapidly to how exciting the world around her is, she is just desperate to express herself NOW and stumbles over the words. So don't panic that she has an actual stutter -- this may simply be the normal stage of "so excited she cant' get it out just yet."
If you really remain worried, ask for a referral to a pediatric speech therapist but please be open to the idea that this isn't a stutter but her brain going faster than her mouth is currently capable of going.