In that case I would ask what
I can do to make it easier to work better with my boss.
How my boss feels is not my business unless she chooses to tell me. What I can do to make our relationship better IS. It's not as if I could DO anything about the way she felt, just by
knowing how she felt. If she is in the middle of some ghastly family situation, say - I can't fix that. But learning from the cards that she needs an hour's peace before she is approached in the morning would be something I could do that would make life easier for us both.
That isn't the same thing as using the cards as a self-help tool - it is more using them as a general advice tool.
IF the cards - when asked how I could help her - said unequivocally, as part of the reading, that she was cheating on her husband - that would not - in my view - be the same as asking the cards directly if that was the case.
I think tarot is of most use as an aid to living the best we can. Knowing things that other people choose not to tell me is no particular help to me. That's like the old "eavesdroppers never hear good of themselves."
ETA the OP asked how ACCURATE such answers would be. THAT I don;t know, but I have always suspected that if you ask a question about something that another person is hiding, the answer is likely to be dodgy, coloured by the very fact that they are hiding something. I haven't had the opportunity or the inclination to test this, though.