“Can stuttering be fixed in kids?”

There are a lot of factors regarding stuttering. In general, stuttering cannot be "fixed". Children can grow out of it, but it depends on their age and a lot of other factors. I would recommend that you contact a Speech-Language Pathologist for further assessment.

How old is she?

There is no known cause for stuttering. Some persons grow out of it and some maintain a dysfluent pattern consistent with the stuttering diagnosis for a lifetime. Everyone is different. Definitely consider an evaluation with a speech language pathologist to determine if there is a true stutter happening and strategies you can work on to generate smoother speech events.