Eggs are fine.
The fat content in the yolks can be a concern for some dogs, but it should be okay. When in doubt, just use the white.
You could also try low fat, low sodium cottage cheese, yogurt, sweet potato, etc.
Because egg in and of itself is not a balanced diet for a dog, you could just consider it a treat. However, problems can occur when unbalanced, homecooked food makes up maybe about 10% of a dog's diet. So I'd make sure that doesn't happen. One egg over three days doesn't sound like a problem to me.