Mountain was born and raised in Hong Kong. She completed her primary education at
Peak School and then enrolled at
Island School. Mountain began playing hockey at Island School where she captained the school team and joined the junior Hong Kong field hockey development programme. During high school she was named captain of the Hong Kong U14, U16, U18 teams. After high school, she went to the
University of Birmingham, where she graduated with a Bachelor of Commerce (B.Com.). At university she continued to represent Hong Kong at field hockey. ==International career==