For years, I've struggled to make friends due to feeling socially awkward and struggled to make friends I can be close to and call her my sister. If you look at it this way, most friendships don't last and very few friendships turn into such a close bond you can call each other sisters.
I met my best friend in the fall of 2018 and we talked for a year. We have just recently started calling each other best friends then sisters. The fact I could have the lifetime privilege to call my best friend my sister is not as common as you think. If you look at it from my personal experience alone, I had 3 past best friends but either I did not feel a bond or it ended badly due to bullying.
My best friend and I share so much in common and is another contributor to how we can be this close. She helped me grow to be a stronger person and we share the interest in all forms of art together.
Life is very short and for all the women out there saying they feel alone, there is someone out there that actually cares and can take time to find that right person. Factors to call your best friend a sister can include a natural bond, common interests, care, compassion, respect, forgiveness and the love for one another.
My advice to achieving this important part of life is to get to know her and see if she falls under all the characteristics I listed above.