Anonymous wrote:"Let me ask this again" does make it sound as if she asked you something and you either didn't answer or your answer wasn't clear.
Maybe she means something more benign, like "a quick follow up question...", but I would be annoyed. Depending on how often you interact with her, I'd probably talk to her about it. Or call her on it, "Susie, you wrote, "let me ask this again," but I looked back through my emails and do not see where you asked me this before and I know we didn't speak about it. Can you please clarify whether you ere just using this phrase as a figure of speech? This comes up from time to time and I want to make sure we are on the same page."
PP here -- this is assuming her question was clear and your answer was clear (as PP noted). If one of you isn't communicating well, then address it differently.