Final answer:
Helen's attachment to her mother is secure because she prefers her over a stranger and uses her as a secure base to explore the environment.
Step-by-step explanation:
Helen's attachment to her mother can be classified as secure attachment. In secure attachment, the child prefers the parent over a stranger and uses the parent as a secure base to explore the environment. Securely attached children are distressed when their caregivers leave but are happy to see them when they return. This type of attachment is the result of caregivers who are sensitive and responsive to the child's needs.