Small Bantam with runny nose and sneezing/coughing

I have this small Bantam hen, who recently just started to cough/sneeze and has a running nose. The nasal discharge is clear, so I'm not sure what to do. I've been keeping an eye on her and the other two hens (which are copper Marans) and she's the only one who's doing it. She's acting completely normal, still laying she's not lethargic at all, but she just is sneezing. I don't know if this could be the cause of the weather right now where I live, that has started this reaction (because a few of my rabbits are doing the same thing) but I don't want to have to kill her if I don't need too. I just need to know if this is something I should be worried about spreading to my other two hens or what. Any help would be great, haven't been into the whole chicken thing for all that long.