Sympotoms of a sick chicken?

[Chicky Crazy]

I have a two year old Plymouth Rock that lately has had a squeky voice. I ask and you said she was ok but that I should watch for any other symptoms. Right now she has a dirty but, and a sometimes pale crown. Is she sick? Today I let her out and she kept going in and out of the coop, making the really loud, high pitched noise that they make before/after laying a egg, until she finally laid an egg.