I'm certainly no expert, and if you're really concerned, have it checked out, but I seem to remember my kids doing some stuttering in the beginning and at the end of words at around this age. It's almost as if their brain is going too fast for their mouth, so the stuttering slows them down a bit and allows them to catch up. I think that sometimes it happens without their realizing it and other times they play with it because it's fun. Don't make a really big deal about it with her unless you want her to do it all the time,
but keep track, and as I said--if you're worried, then see a doctor. Mom knows best!