I treated my budgies 3 weeks ago with Ivermectin for scaly face but one budgie has not improved. Should i treat again or wait a bit longer?

Do you have a picture Deb? Is it a hen or a cock bird?

Its fine to treat again Deb.

I will treat again then. Here is a picture of her but i am sure it is scaly face that she still has but maybe i am wrong.

Wont do any harm to use the spot on again Deb. Especially if you think the others are better from it than she is.