Final answer:
The therapist should guide the child's behavior in a positive manner and teach them appropriate ways to express their feelings.
Step-by-step explanation:
In this situation, the therapist should play a role in guiding the child's behavior in a positive manner. The therapist should not ignore the doll, as this may reinforce aggressive behavior. Instead, the therapist should encourage the child to play nicely with the doll and teach them appropriate ways to express their feelings. For example, the therapist can demonstrate how to have a calm discussion or use non-violent problem-solving techniques, such as compromising or taking turns.