Posting a picture of her would help a ton. It sounds like she might be egg-bound, or she may be in shock. Try taking a look at her vent and see if there is egg dripping out. Or if she is breathing heavily. You say that her legs are moving but she can't stand or walk. Can we get a picture of her legs? Did she leave the coop this morning? You went out to check on her a few times throughout the day, why is that - did you see that she was acting differently this morning, or did this behavior just occur.
Are her eyes bubbling or foaming? Any discharge from the nose?
Sorry for all the questions, but they may help get to the root cause.
I am no expert - so hopefully, someone here can help you out!