She (from my personal observations of knowing people with speach impediments)is probably the active type; thus, probably symptoms of ADHD; meaning she has a lot on her mind but not able to get it out. Also, children tend to do what they LEARN. Meaning, she knows she stutters.
She (in her litTle mind) has accepted this without knowing it.
When she starts to speak, pay close attention to what she is saying, be patient, and let her know that it's o.k. to speak s-lo-w-l-y, so that she can get out what she is trying to convey. It will let her know that you understand and that you care because you are willing to listen to her.
Pretty soon, she will GAIN CONFIDENCE and notice that she does not have to stutter, and should grow out of it.
It might also help for you to speak speak along with her when you know what word or words she gets stuck on so that she can get over the verbal 'stumbling block(s)' and continue normally.
Hope this helps out a little.....
sincerely,
L..