Why yin and yang? It is the symbol of Taoism. Simply, Taoism is to put into practice higher understanding, not only by mentality but also physicality. It is true balance to supersede attachment and become the flow.
She is yin, a protector and representation of compassion and support. She is placed on the left side of an entrance, if you were on the inside facing out. She protects all and everything that resides in a building. Traditionally the female (yin) and male (yang) foo dogs are placed on opposite sides of an entrance for complete protection. They have been used in China since the Han Dynasty (206 BC – 220 AD) to protect temples.