I had a Black Copper Maran, that turned into the Mad Hatter. You could see it in his eyes, he was attacking everyone adults to my grandkids , I couldn't even walk by the girls with out him attacking me. Since I got ride of him all the girls are more relaxed, friendly and they've been laying...
There's no eggs withdrawal with Safeguard, I wouldn't use any of the egg for hatching, I would think atleast 3 weeks after last dose to be on the safe side.
Thankfully I have a son inlaw that will do this for me. I remember my grandma in one hand the chicken the other hand an axe and take them to the stump. I have the problem of hesitation where I would do more harm then ending it quickly.
Maybe some prebiotics and probiotics to help get some good bacteria in her crop, I use Predue Thrive and Recovery 911. I get them off Amazon, if you're able to get it Canada.