You could always order just females and after they are 4 months old they can go in with the drakes and hopefully, she will have a better chance of not being the favorite any longer. Make drake jail many here do this to protect their females over breeding season.
Wrap her in a towel so you have better control and try some saline compresses on her eye. That should help loosen the gunk. Or just some warm water compresses. Removing her from the drakes and letting her recover is going to help a lot. 10 yrs. Bless her heart. I have 3 Muscovy females that I am...
Drakes grab hold where it’s convenient which means eyes can get injured. You need to remove her from the drakes and start treatment. I hope your TSC has the Terramycin.