Rhode Island Red with leg issues :(

So I have a sick Rhode Island Red hen, she's so sweet and I love her so much and I don't want to lose her because she's extremely docile and I don't have many hens like her who are willing to sit on my lap and petted. I think she has a sprain in her leg, I don't think it's broken at all becuase I've given her a half exedrine pill and she walks around like nothing's wrong, I don't want to continue doing this because I don't want the leg to not heal itself. Right now I have her in a cardboard box with wood chips, food, water, and plenty of sun. I'm not exactly sure what to do to keep her alive or help her heal so she can be a free walking happy hen again. Would the best option be to put her down? I really don't want this unless it's a last resort because I love her too much. Please help!!!

PS: she's around 4 or 5 years old