Mary, how much money do we have left?
This seems like a normal question.
For the question to indicate that 'do' is used for emphasis:
Mary - just how much money do we have left then?
Then (just) how much money do we have left, Mary?
So (just) how much money do we have left, Mary?
where each time, 'do' is emphasized.
"then' and 'so' at the start of the question indicate that some discussion has gone on before this sentence, where Mary has prevaricated/been evasive or indefinite/has been hemming and hawing; or she has talked about this bill needing paying, and that expense coming up, but doesn't get to the point and say how much is left over.