Kerr is Australia’s record goalscorer and one of the country’s biggest sporting idols.
She has won five consecutive Women’s Super League titles, three FA Cups, two League Cups and the Community Shield at Chelsea.
She signed a new two-year contract in June but has not played since January because of a knee ligament injury.
Mewis, who has won 53 caps for the USA, joined West Ham from NJ/NY Gotham FC in December.
In March Kerr pleaded not guilty after being charged with racially aggravated harassment of a police officer in London. She is scheduled to appear in court in February.
