In addition to adding a frame of eggs/brood, realise you may not be
queenless.

    Ask yourself what conditions may lead to an eggless, broodless hive.

    1) A queen not laying eggs.
Because:
      A) No Queen
            1) killed by beekeeper accidentally
                    (why didn't they build supercedure cells?)
            2) Killed by bees
                    (why didn't they build supercedure cells?)
            3) Swarmed out and not replaced
                a) virgin queen killed by myriad of means
                b) virgin queen was faulty
      B) No fertile queen
            1) swarmed out and replacement vigin was killed
            2) swarmed out and replacement virgin unsuccessfully mated
       C) Fertile Queen is present and does not lay
            1) Too cold for brood (doesn't sound like it)
            2) Queen instinct is that it is the wrong time.
            3) Queen is diseased
            4) Queen is otherwise defective

These are only some of the major reasons why a hive will appear
queenless.

You must decide which is pertinent here. In any case I would be sure to
feed plenty of 1:1 sugar syrup just in case the queen is being fed honey
and her instincts tell her there is no honey flow on and that new brood
is not necessary. Workers will become defensive if there is no other
work to perform. Tracheal mite infestation has been found to lead to a
decreased capacity of the queen to lay. If you can, It may be a good
time to treat with menthol to check this possibility as well.

Thom Bradley
Norfolk, VA area