Hi
I'm sorry your hen is sick. Poor girl she does look unwell. When you say her "stomach" is tender and feels bloated, do you mean her abdomen between her legs where her intestines are or higher up in the crop/gizzard area? Chickens don't have a stomach as such, so just want to be clear... Also, it might be a good idea to check her crop is emptying overnight by removing access to food when you go to bed and checking in the morning. Did she poop a more normal poop after you did an internal exam for egg binding? Is there any swelling around or below her vent?
How much bird seed do you add (percentage)? Mixing seeds/grains with layer feed is not a good idea. Hens will pick out the bits they like and leave/waste the less favoured bits which are often the ones that are best for them and it can result in a dietary imbalance which can lead to surprisingly devastating health issues. Not saying that is the case here with so little information so far but it can be an issue. Layer feed is a complete feed formulated to provide everything the bird needs to remain healthy and lay eggs. Once you start adding extras it is easy to tip the balance. More than 5-10% extras on a regular basis and you are likely to have problems sooner or later.
Do you know when she last laid an egg and if so, was there anything unusual about it?
My gut feeling is that she probably has a reproductive disorder. Being a high production bird (she is actually a red sex link not a RIR) they are prone to such issues once they get beyond 3yrs. If it is abdominal swelling between her legs, it may be salpingitis or possibly internal laying and/or EYP.
I would give her a direct dose of poultry vitamins like Nutri Drench and keep her warm and assess whether her crop is functioning correctly overnight. She might benefit from a chicken sling to keep her up out of her poop. Something like this can be easily put together...