Leghorn can barely stand up properly and hasn’t laid in over two months she started molting around 2 months ago and has a huge bump on her vent but isn’t egg bound.
Her molt could have made her weak or brought on these symptoms. Does her belly feel firm, soft or like fluid inside? Reproductive infection, salpingitis, fatty liver disease, or water belly are some causes for an enlarged lower belly. Those can also affect walking or standing. I would place her in a basket or dog crate and position her on rolled towels. Offer some fluids, and electrolytes or Gatorade would be good. Poultry NutriDrench or Poultry Cell are good to give orally 2 ml. Offer moistened feed and some scrambled or boiled egg. Let us know if her crop is empty and flat or full, firm or puffy. Check her for lice and mites on her skin when you have time. Has she been eating, or could she be dehydrated and getting no food from her condition? Let us know what you can.