Your hen appears to have a compromised immune system. What that means is she may not have the strong cells in her blood to fight off secondary infections, her respiratory issues being just one of many. She may rally with the steroid and get past her respiratory infection this time around, but she may not be as successful with future infections.
Most flocks with chickens that live for more than a few years as in flocks where they're raised as meat, can develop infections of various kinds as normal aging affects their immune systems. When you add on the burden of carrying an avian virus, it can further take a toll on immune systems. I've lost more hens to reproductive infections than directly because of the leucosis virus.
No one can say whether your hen will kick her infection this time and go on to live another few months or even a few more years. It's all up to her body and whether she fights this off or not. The signs are that she has a chance to live a few more months, but her long term prognosis isn't encouraging.
What you can do is give her, as well as your entire flock, the best care and feeding you can in order to maximize their health and their immune systems. I do this by keeping an immaculate coop and run to reduce the bacteria they encounter and must fight off, and I feed fermented feed which maximizes nutrition they derive from their feed. These strategies give their immune systems all the help they can get.