this chicken in question was laying just fine during winter - about every 2 days. Then she started walking weird and wouldn't lay eggs.
What are your chicken keeping goals? If for production, then cull the hen. Leghorns often burn out due to high production. That walking funny and not laying eggs ... she's not doing all that well. Perform a necropsy and take a look inside, next time you have a hen with similar symptoms, you may consider putting them down once you see what's going on.She still walks really weird and won't lay eggs through.
IF she's a pet and you want to prolong her life for a while, then feel her abdomen below the vent between her legs. If there's fluid, then drain the fluid. This can make them more comfortable for a short period of time. Antibiotics can help with infection for a little while as well. Offer daily supportive care. See that she's drinking and eating, check for lice/mites and treat accordingly (unwell hens do not dust bath that much and can become infested). Make sure her crop is emptying overnight. Monitor the abdomen every other day and see if there's fluid buildup, if there is drain again (if you needed to in the first place). Once she's in a state of decline after all the care you give her and she's starting to struggle to breath and can hardly walk - consider putting the poor thing down.