You might try Pfizer Terramycin Opthalmic Ointment, 1/8 oz. I got it at TSC and it comes in a small tube. Just before using the ointment apply a warm used tea bag to his eye for 5 minutes or so.
I was looking around for muscovy babies for sale and came across this from Ugly duck farms
Coccidiosis
Muscovy aren't like other ducks. Coccidiosis is rare in normal ducks, but quite common in Muscovy.
Coccidiosis live in dirt. Grass clippings, dirt baths in the yard, and dabbling in mud...
Your peeping tom fil is at best an enabler. If he didn't at minimum permit it she wouldn't be that way. If the water hook up you're talking about is public, I would look into the cost of having a well dug. In Michigan, at least, a 160 foot well costs about $6000 and no monthly water bill...
Is selenium deficiency a problem with chickens? Is the feed medicated? I would try a good multiple vitamin/mineral and substitute ACV in the water instead of electrolytes for a week & see if she seems better. ACV 2-3 teaspoons per quart of water. What does her poop look lie? Could it be cocci?
I have got a really nasty gander, he year round attacks whenever I get within his striking distance, which varies on his mood. He attacks when I go to feed and goes after my hand or legs even when I try to shield with the food. I want to just bat him across the yard but don't want to injure...
A lot of people trying and failing to raise orphans is how we gained the knowledge that saves thousands of orphan animals/ You do the best you can and learn from it so their lives weren't wasted.