Dawg53 describes the best way to give medications in the link below. Direct dosing is much easier than trying to get them to eat bread with medication on (they KNOW you want to them to so they don't:tongue). I would try deworming to see if that helps.
She may have something else going on...
I would definitely check her crop to make sure it's emptying as suggested.
Any chance she ate moldy feed?
Can you get a photo of what she looks like, how she stands?
Where are you located in the world?
Gapeworm is fairly rare, but Ivomec is not a good choice for treating them. Valbazen or...