Well, that is kind of what my chicken acted like before she was diagnosed. She would also sometimes be standing and her head would drop to the ground like she was falling asleep or just really, really weak. I would take your chickens to the vet and have her listen to their hearts.
Eventually, what happened with my hen (she is still alive!) is that she got a prescription for Elanapril from a compounding pharmacy, then we added Lasix. It seemed to help, but what REALLY helped is that she eventually got a Deslorelin implant to stop her from laying eggs -- due to a totally unrelated problem. She wound up with an impacted oviduct and had to go into surgery to remove the impaction. (Super risky with a heart failure hen, I know.)
Anyway, since the burden of egg production was lifted from her, the change in her energy and overall health is unbelievable. She is back to her old, pre-heart-failure self. Like, I would never guess there is anything wrong with this chicken, she is acting so strong and vigorous.
I don't know why the implant helped her so much, but it's like a miracle. In case you're wondering, it's about $200 and it's supposed to last 3-6 months. I have another hen with the implant, and it lasted a full 6 months.
But I guess the first step is getting her to the vet and determining if there is heart failure. The Elanapril kept her going for a while. I still have no explanation for why the Deslorelin implant helped her heart failure, but it was really a dramatic and immediate change.