The person you are describing exhibits a common personality trait known as ambiversion. Ambiverts possess characteristics of both introversion and extroversion, but their behavior may vary depending on the situation or the people they are interacting with.
In the case you described:
Introvert Around People She Doesn't Know: When this person is around unfamiliar individuals or in new social settings, she may display more introverted traits. This could include being reserved, quiet, or cautious in her interactions. She might feel more comfortable observing and listening rather than actively engaging in conversations.
Extrovert to People She Knows: Once this person is around people she knows and feels comfortable with, her extroverted side emerges. She may become more outgoing, talkative, and expressive. With familiar individuals, she is likely to feel at ease and may be more willing to initiate and participate in social activities.
It's important to note that ambiversion is a natural and normal personality trait. Many people fall somewhere along the introvert-extrovert spectrum rather than being strictly one or the other. This flexibility in behavior allows ambiverts to adapt well to various social situations and enjoy the benefits of both introverted and extroverted characteristics.
Ambiverts can have the best of both worlds; they can appreciate and value time alone for reflection and recharge (like introverts) while also enjoying social interactions and forming connections with others (like extroverts). The ability to shift between these two modes of behavior can be advantageous in navigating different social contexts and building diverse relationships.