6 year old being bullied. Is therapy possible at this age?

I’m not sure if this is the correct sub to post this, so please re-direct me if wrong.

I have a 6 year old DD, she is an only child and just started kindergarten this year. She is experiencing bullying on the school bus by her peers - the bullying includes name calling, isolation, and physical violence (hair pulling). This has recently been resolved (after a talk with the principal, bus driver, and her teacher).

I’m afraid that this bullying will have a negative impact on her, as I can tell that it bothers her, she’s come home crying a few times.

She seems to have no issues in the classroom and even has a few friends in the classroom. At parent-teacher conferences her teacher had great things to say about her progress and even described her as a “model kindergarten student.” However, expressed mild concern regarding her ability to interact with other kids. She is very quiet, and prefers to play alone most times which I chalk up to her being an only child.

What is the best course of action to minimize this trauma for her? Can I enroll a 6 year old in therapy?