"There is an antisemitism problem in Labour," she wrote, adding Mr Nardell's appointment left her with "no faith in the objectivity of the process".
She called on the NEC, the party's governing body, to "urgently review his appointment".
Supporters of Mr Nardell have defended him.
On Friday, Naomi Wimbourne-Idrissi, the founder of the pro-Corbyn Jewish Voice for Labour, told LBC Radio the lawyer's critics “will only be happy if we have a QC in the pocket of the Israeli Embassy".

Host Nick Ferrari labelled her assertion "ridiculous".
Ms Wimbourne-Idrissi also urged the party to formulate a definition of antisemitism which draws a distinction between "abhorrent hostility and hatred of the Jews and attitudes to Israel".
David Collier, a vocal supporter of Israel whose research exposed examples of Labour antisemitism, tweeted: "Dear Naomi - you want an example of antisemitism in Labour - that quote of yours is a good one."