I wonder how the sanctuary could know they were 4-5 years old? Since they were being chased when they were rescued, I would lean more toward the limp being an injury or sprain. I would not give any more aspirin. You want her to limit her activity to give the injury time to heal. I would probably keep her from roosting by keeping her in a dog crate at night, or by being there to place her on the roost in the evening, and take her off the roost in the morning. Something else I would recommend would be to give her 1/2 tablet of human vitamin B complex crushed over some food daily. It also dissolves in a little water to pour on food. Any brand is good.
https://pics.drugstore.com/prodimg/356052/450.jpg
https://pics.drugstore.com/prodimg/356052/450.jpg