Use the Johari Window approaches (hidden, open, unknown, blind), apply it to the information about your best friend with this information:

The way I describe my openness to her is as "we don't keep secrets from one another."This quadrant represents the part of our relationship where we both have shared information, experiences, and feelings. We've been friends since fifth grade. We have shared memories and have had deep conversations about our lives, hopes, and dreams. This quadrant is where we have built trust and mutual understanding. Meaning, we have always vowed never to keep secrets from one another and to always be honest with each other. In contrast to my roommate, she was the first person I texted when I discovered my mother was having surgery. A strong friendship stems from trust between the two of us.