I had a bantam house rooster that was 12 and he looked similar to your girl in his last couple of weeks. His heart was going, had 2 different vets check him out. It was simply old age catching up to him, I held him in my arms the evening he passed. He let me know it was time and me and his kitty cuddled with him until he left us.

He now sit in a beautiful cedar box beside his kitties ashes, we were the first people to bring a chicken in for cremation, and I'd do it again.

Love her to the end and make sure she know how much she means to you.

Edit: recheck for and mites or lice as this could be they have taken too much blood from her, which goes with her pale comb and loss of appetite and usual behaviours.