I would let her stay out and be as active today as she feels like. It does seem like she may have sprained something, foot, ankle, knee, or hip. Azygous has a good suggestion to look for green bruising tomorrow, as well as any swelling in a joint. I would not use a sling on her, since they can injure themselves trying to escape them when they don’t need to be in them. Those are more for extremely lame or disabled chickens.
Tonight, you may want to place her on the roost if you can come out in the morning to get her off before daylight. Or cage her this evening with bedding. If she is worse tomorrow, you could limit her activity in a pen or dog crate with food and water. If you have lots of money, an xray could rule out a fracture, but sprains are more common. They don’t really measure aspirin in grains anymore, but in miligrams. 81 mg equals 1 grain, and 325 mg equals a 5 grain aspirin. If you use aspirin, it can cause bleeding of the GI tract after 3 days. Vets can prescribe meloxicam, and anti inflammatory drug.