So twice now I’ve felt between her legs under her vent and she has passed gas. O’s maybe something she ate? Fungal?Welcome To BYC
I'm sorry that your hen is not well.
Can you post some photos of her and her poop?
Can you feel her abdomen below her vent between her legs - is there any bloat or feeling of fluid?
Has she ever been wormed?
I'm not sure what's going on with her. You are doing what you can for her. I would be inclined to give her 1/4 tablet B-Complex and 400IU Vitamin E once a day.
She may be suffering from disease like Marek's. I know @microchick has experience with Marek's. Possible molting was a stressor to bring on symptoms even in a older bird.
She might benefit from being placed in a sling for short periods of time during the day. This will get her upright and she may learn to move her legs more.