possible merricks disease or avian flu in sick laying hen?

today one of my laying hens is very sick and is not acting herself. she was perfectly fine yesturday happy, alert, and walking around with the others like normal. today i went out to clean the coops and she was just sitting inside the big coop in the back. she had her feathers all ruffled up and would not walk or stand up on her own. she had her toes curled up on her left foot but not her right. she leans to one side and is using her wings for support. she seems very tired and does not want to eat her layer pellets (Dumor layer pellets) and is drinking a lot of water. i also noticed that she is having trouble seeing in front of her, i say this because when she would go to peck at some yogurt i had or some fruit she would reach to far or miss it completely going towards the side of the food and water dish. her stool is very very watery and has a bad smell but it is not overwhelmingly strong. i brought her inside to warm up and to get her away from the rest of the flock in case it is contagious to the rest of them. she usually lays in the winter but the past couple days she has not layed any eggs at all. i have looked at different diseases in chickens and im not sure at what it could be. i was thinking either adult merricks disease or avian flu or she could have swalloed something that is making her sick. none of the other chickens are showing any symptoms of being sick or have any changes in their normal behavior. she is 1 1/2 yrs old and is free range. i am going to keep her in the house away from the others until she gets better. i would take her to the vet but i live with my parents and they wont let me take her because they see her as 'just a chicken' and not worth it. she is a pet and i would take her asap if i could but i am being held back from doing that. does anybody have any ideas as to what it could be that is making her sick and any advice as to what i can do at home to help her get better? i want only serious answers, no comments about killing and eating her because i will not do that.