Answer: ADD/ADHD
Step-by-step explanation:
ADHD which is know as Attention-deficit/hyperactivity disorder is a disorder noticed in people who are very restless in every situation themselves and rarely concentrate but are rather always excited and jump or play at important moments you might want them to be calm.
ADHD, begins at the tender age of children and becomes worse if not controlled it monitored then. This is what's affecting Sierra.