Impaired motor function can be caused by various things. It's important to investigate where your hen may have been on Sunday or Monday. Was she confined to the run the entire time? Or has she been free ranging on your property?
If free ranging, you need to walk over every inch and look for anything of a toxic nature such as machinery leaking fluids onto the soil, recent treatment with insecticide, poisonous plants or mushrooms, or soggy, moldy compost.
If confined to the run, you need to inspect the feed for mold. Recently I had a big bag of newly purchased feed that had been contaminated before I bought it. The feed at the bottom of the bag was dark and putrid, smelling like rodent piss and had formed hard clumps. Grain mites had multiplied beyond anything I'd ever seen. Purina heard from me. Luckily, none of my chickens got sick.
Besides a toxin, your hen may have an avian virus that is producing these symptoms. Marek's comes to mind. Also, she could have coccidiosis or an infection from bacteria she picked up somewhere.
You may be beginning to see that there are a lot of possibilities. Until you can identify what could be making her sick so you hopefully will be able to treat it, you need to keep her hydrated, even if you need to force water into her with a syringe.
To rule out a crop disorder, check her crop first thing in the morning to determine if it's completely flat and empty.