My sister and I fought our entire childhood due to our differences. As adults, we are best friends.

The author (left) and her sister didn't always see eye-to-eye when growing up. As adults, they've grown closer.

Courtesy of Rachel Garlinghouse.

• Growing up, my younger sister and I had some epic battles, with both of us showing our mean side.
• Over the years, our relationship evolved from a sibling rivalry to a strong adult friendship.
• The things that once drove me nuts about her, are now the qualities I love and appreciate the most.

I am the oldest child. Like many...