At this point, where she can barely stand up, she is probably not eating.
I would feed her something in the beak, with a syringe. I am no expert and not sure if what I did was ok, but I did two things:
- I fed my sick ones some water mixed with chick feed
- I fed them liquid nutrition for humans, to give them proteins and carbs.
When you do that, you don't want to put too much food in the beak at once or else the hen might aspirate the liquid. I just put a few drops, give the hen a chance to swallow, and continue on.
Another thing I did was to put pillows or towels on the sides of the chicken so it remains in sternal position (not fallen down on either sides). Not sure if this applies to chickens, but with other animals that are a bit heavier, they can get lungs or legs problems if they are laying on their side for too long, so that's why I tried to keep mine straight.
Good luck.