Mountain began playing hockey at Island School where she captained the school team and joined the junior Hong Kong field hockey development programme.

She has played at numerous international tournaments including two Asian Games,[3] two Women's Hockey Asia Cups, two East Asian Games, and two Women’s AHF Cups.

Mountain joined Hong Kong Football Club when she was 15 years old and at the age of 20 she captained the team for two back-to-back seasons (2007/2008, 2008/2009), winning both the premier division title and knock-out cup competition.

She has won six premier division titles and knock-out cup competitions with Hong Kong Football Club.

From 2016 to 2018, Mountain played hockey for Singapore Cricket Club and captained the team to win the premier division in 2017.