I have a few friends who live in France, so whenever we talk online, we always try to write in French. During one of my first French classes, I think I remember my professor saying that, with no exceptions, one must include the subject pronoun when we speak or write. But I've noticed my French friends often exclude the pronoun. For example, I wrote to my friend, "ma famille et moi, nous avons déménagé à Seattle," but afterwards, I thought it sounded repetitive to include "nous" because "ma famille et moi" was obviously the subject. Another example would be, "Ma sœur, elle a 21 ans". Is "elle" necessary? Any help is appreciated!