Hen can't stand but looks well

[Woodlands1]

A week ago my chicken struggled to stand, although she could still hobble a bit. A couple of days later she couldn't stand at all. Other than her not being able to stand, she looks perfectly fine. She is bright and alert. I can only tempt her to eat fresh corn though. I have checked to see if she is egg bound but cannot feel anything. I have started her on a course of antibiotics and liquid calcium (although I were already feeding her oyster shells) and removed her from the other chickens. Can anyone give me any advice as to what this could be and how else I could help her.