Since you've lost 3 in a short period I would strongly recommend you have one necropsied. If you lose this hen/pullet, then that would be the best way to know exactly what's going on. There are virus's that can affect the flock, and symptoms may or may not be the same bird to bird. It's also possible that it's bacterial or they got into a toxin somehow. Spoiled feed, leaking machinery, something rotting, and sometimes toxic plants if they range, are all possibilities. Marek's disease also has to be considered. I will link to necropsy resources by state, find your nearest and call for particulars. In many states it's quite reasonable, or even free. The call won't cost you anything, to find out. If you are close enough you can drop them off rather than ship, many times. If you lose her refrigerate the body, don't freeze it, and get it there within the time frame they specify. Whichever is closest to you can tell you specifics. It's a good idea with multiple losses to find out for sure what it is, in case it may affect the rest of your flock. Or get peace of mind that it won't.
https://www.metzerfarms.com/poultry-labs.html
https://www.aphis.usda.gov/animal_health/nahln/downloads/all_nahln_lab_list.pdf
Can you post a video of what your hen is doing? You have to upload to another host, like youtube, and put the link here, then it can be seen. It sounds like maybe wryneck symptoms, or something else neurological. That can be vitamin deficiency, head injury, or disease based. Usual treatment is Vitamin E with a bit of tuna, sunflower seeds or cooked egg for selenium to help with the uptake of the E. I would also give her a B complex or Super B complex tablet or capsule daily, the B's can also cause odd neurological symptoms. All of those can be human supplements from any pharmacy or big box store, easy to find that way, and vitamins are vitamins. The B's are very safe, extra is excreted, so no worries on too much. E if given for too long can become toxic, but you are fine for several weeks, usual dose of that is 400iu, you can poke the capsule and squeeze the contents into her beak.
Link below on wry neck.
https://www.raising-happy-chickens.com/wry-neck.html