I think Laddy was in a similar state - no conditions ripe for aspergillis, yet, for some reason he picked it up. And it is everywhere, pretty much, I feel. Any of us can get run down.
Gosh I wish I could be more help.
http://www.majesticwaterfowl.org/mmissue121.htm Laddy's story in here.
The problem may be aspergillis, in which case the anti fungal would make sense. There is a Majestic Waterfowl newsletter about Laddy and asper - you may want to look that over.
I would have a fecal done, as I prefer not to deworm unless there are worms. I took Carmella in when I thought she...
The ACV with the mother should be fine. Dosage wise, see if @casportpony can offer help. Our ducks were given Tylan a while back, and it was
1/4 teaspoon powder per liter of water for seven days.
I believe it was Tylan50.