Help with our very sleepy chicken please :)?

Chickens can be very fickle. They can actually have a heart attack. The falling asleep could be extra stress. Have you and your sister spent time with martha? Have you held her? She just may be having some trouble adjusting. Is their enclosure very different from the one she was in at her previous owners house? If she doesn't have adequate area to rest, she could be suffering from fatigue as well. Make sure that she goes to "roost" in the evening with everyone else. If they dont have a good place to sleep, that could definitely be an issue. Best of luck with martha.