It's quite odd that it's somehow marginally more acceptable to be antisemitic than to be racist about blacks, or even homophobic. If LW is feeling like a coward, it's because he is one. Not that I don't understand his situation.

Some options:

Find another job.

Start documenting these instances. Then get a Jewish friend to apply for a job. Note any comments made about this applicant. When applicant is rejected, go to court.

One-up her. When she makes comments on a Jewish client, state that you agree, and will not work with them anymore. State that she should make it company policy not to purchase goods or services from Jews (why make them richer?), to sell goods or services to Jews (why have to deal with those arrogant Christ-killers?), or to employ any Jews.

Explain that you are in the process of converting to Judaism.