Oh my. We have hatched about 1500 chicks with momma hens so probably about 150 times that we have set eggs under broody hens. We have had bad mommas that didn't cluck the food, were over protective, not protective enough. We have had ones that broke set and abandoned the eggs. We even had one that killed other hens chicks. But we have never ever had one that killed her own chicks.
Did a search on the topic and found this that might be of some help
https://www.hobbyfarms.com/when-a-good-broody-hen-becomes-a-moody-mama/ I guess I would keep a good watch on her and if she attacks another chick remove them as soon as they hatch or even as they are hatching. I hope you don't have to do this because raising chicks with momma hens is so much fun. Being day 19 something likely wasn't right for the chick to hatch and it may have died on its own and she was just getting some nutrition from the dead chick. But if it turns out she is an evil mom I guess I would put the piping eggs under a heat lamp or heating pad. Use a thermometer to get the temp as close to incubator temps as possible Never used an incubator myself but one web site gives these temps. I
- Optimum temperature: 100.5o Fahrenheit
- Temperature range: 99-102o Fahrenheit
- Don’t let temperature drop below 99o Fahrenheit
- Do not allow temps of 102o Fahrenheit to last more than a few hours