Hey, I'd like to let you know that 3 years old is the typical onset for developmental stuttering. Stuttering has a genetic component. It is likely the reason she has developed it, even if yourself or partner don't stutter. Genetics is the main reason for stuttering to arise for most of us too. Lastly, around 80% of children who begin to stutter recover on their own and it is more likely for girls to recover than boys. This means it is very promising for your daughter to recover on her own. Nevertheless, when in doubt, follow the guidance of the speech therapist. All the best.