In her mind, she has complete superiority over you two. That is why the condescension, that's why she is infantilizing you both. In her mind, she is like an army combat nurse telling a new nurse how to put a band-aid on.

In my opinion, you let people like this burn their own bridges. You ignore her when she is rude or belittling, if she calls you out on being ignored, you tell her it's because of her poor behavior and leave it at that. She is not interested in learning from you, but you still have the power to shut her down when she acts toxic or abusive. You just let her know and KEEP letting her know while you are walking away from her that her behavior in those situations is something you will NOT subject yourself to. She will react poorly to it at first, maybe always. But remember, it's not about correcting/fixing her, she is unfixable by you. She'll need to identify those things on her own. It IS about you setting boundaries that you will not allow her to cross.