Is it ACTUAL stuttering "m-m-m-m-m-m-m-m-m-mommy come l-l-l-l-l-l-l- SEE this"
Or partial/whole word "stuttering" (which isn't) "mom-mom-mom-mom-mom-MOMMY come look at this!"
The partial word thing is normal, natural, and common. It's caused by 1 of 2 things. Either her mind is racing ahead of her mouth, and she has to catch up (later on, the partial word will be replaced with the UBER irritating "ummmmmm") OR she's feeling rushed/nervous (usually by feeling like she has to talk quickly or will lose her "audience" or by adults being impatient). The whole "spit it out" or "hurry up" is the WORST thing you can say/attitude when this happens. It makes the problem worse and more frequent.
The way to combat partial word stuttering is to ignore the world, get down on eye level, smile, and say "I'm listening" both verbally and with body language (eye contact, smile, etc.).
The partial (or whole) word repeat thing has a clinical name I always forget (my godmother is a speech pathologist). It is VERY different from real stuttering, but most parents just hear the repeat and think "stutter".
If it's a REAL stutter, she'll need intervention. If it's the partial or whole world thing she'll grow out of it as she gets increased confidence.