Hi Poppies.
The Feelings You And Your Sister Experienced When Picking Up On The Atmosphere, Were Picked Up By Your Sixth Sense. It Sounds To Me As If You Have A Strong Natural Ability.

As For The Question Of Body Language. Well I Understand What You Are Saying About Avoiding Eye Contact. It Is True That Confident People Give Better Eye Contact. However, It Is Something More Than This , That Alerts You About Someone Who Has Been Through Similar Experiences. I Believe That There Are Many Reasons Why An Individual May Lack Confidence. For Example, They May Have A Poor Self Image For A Vast Variety Of Reasons.
It Is A Knowing That I Find Difficult To Explain. x