"there is no way a a white privileged rich woman who grew up in Beverley Hills would not know what Shabbat was and all the most basic rules to Judaism, she would’ve been to Bat Mitvahs as well. There is a huge Jewish population in La and loads of them would mix at school etc."
I agree with you to an extent. And if you didn't know you'd ask around friends or google, right?
But I suspect it is written to engage with the broadest possible viewer groups. Netflix doesn't want it to only be watched by groups that are familiar with terms/beliefs or lose their interest because they aren't following the signficance. In this case it has been used within the story.
And it's often the case that you have a character that is unfamiliar with terminology to give other characters an opportunity to explain stuff to them eg Donna/Josh in the West Wing. It means you don't leave any viewer behind.
But yes it is odd that we are supposed to believe this is all new to her.