i take it all back. 10 minutes after i posted that bit about the codeine she woke up coughing and proceeded to cough for the rest of the night.
max daily dose = 1/2 tsp every 24 hours.
in desperation i gave her benadryl again. after a bit though. i figured i should not totally overwhelm her system. it also did not work.
we are very tired today.
but she appears to be clearing the infection, so that is good.