This time of year, it's pretty normal for hens to go through a molt. I can't see her back super well from your picture - it looks like there might be a bunch of new feathers growing in. Is that what I'm seeing? If so, then yes, she is going through a molt. That being said, molting should not affect her balance whatsoever... Hens going through a molt should act pretty much normal, although possibly slightly grumpy because the new feathers coming in can be painful.
Does she have any other symptoms? Is her tail down a lot? Does she sit puffed up? You said she was eating, but is she as enthusiastic about food as normal? Is this the same hen that laid the lash egg?