Thank you all! I called Animal Control and got an answer (Thanks for the suggestion!)
She has a duty to look over her hens and if my dogs end up injuring and/or killing her animals on our fenced property, then we are not liable. It is slightly different if it is unfenced property due to Colorado's open range / fence law.
Excellent! Don't forget to document this conversation and make lots of notes about it. Animal control would be the final authority if your neighbors try anything.