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In a statement of claim, obtained by ABC News, Ms Wu said her former friend made her out to be a "savage person", an incompetent manager and an unethical person in a series of posts on March 5, 2016.
She claims some of the posts were seen by up to 1,000 We Chat forum members.
However Ms Chen launched her own defamation case, claiming Ms Wu published a series of offensive posts about her.
Ms Chen said those posts were seen by at least 64 members of the English as a Second Language (ESL) group at Knox and 24 members of the Knox Mothers We Chat group.
However, if the court does find the imputations are conveyed, Ms Chen said she can successfully defend her conduct because what she had said was largely true.
"And don't forget, the reason why your son got into Knox is because I noticed the vacancy for you and told you and acted as your referee, I even went to the office with you.
Office workers share files through We Chat rather than using emails.
Even conference calls can be made anytime, anywhere via We Chat as long as there is an internet connection.
Chinese messaging app We Chat dominates its domestic market, as its would-be foreign competitors are often blocked in China.
Today, We Chat has removed what could be considered its most “American” feature: a famous photo of Earth called taken from outer space in 1972 by NASA.