Here is some good news about chickens & lead poisoning:
"The effect of aqueous lead acetate given per os to chickens for 35 consecutive days and the effect of lead on interferon and antibody production was investigated. Chickens were found to tolerate levels of lead as high as 160 mg/kg/day without exhibiting clinical signs or hematological changes in spite of very high levels of lead in the blood (6.2 ppm). It is apparent from these findings that chickens are more resistant to lead poisoning than humans, horses, dogs and wild fowl such as ducks."
Basically - chickens are less likely to be brain damaged by the lead.
BUT, I did find some stories online of people whose chickens died of lead poisoning - but they were "full of pellets" (making me think they had eaten more than just one for sure). I would think you would want to feed her something that would clear out her system... others here should be able to point you in the right direction for a recipe. You may want to isolate her in a dog crate or someplace so that you can run a magnet through her poop so you know when the pellet has passed.