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I have to pay for conference rooms for some of my depositions. That is a cost that is mine, and I wouldn't pass it on to the client or court reporter.
What Janet said. This is none of your business, literally and figuratively.
If you must work for this person, I hope you are scrutinizing your paycheck and what it purports to cover very carefully indeed. Given that she has the gall to ask you something like this, I can't help wondering what else she is trying to get away with.