You can try to splint it, but the danger is that she will not tolerate it and will fight to get it off her foot, possibly doing more damage in the long run. I have often found with older birds that the best thing to do is just watch and wait.
If you decide to splint the foot you will need some sort of stiff backing material. I used to use cardboard, but then found this thin, lightweight wood called balsa wood. You can get it at any craft store. Cut your backing board into a foot shape (I actually trace the wounded bird's foot when they are putting weight on it). I like to tape the toes down separately so no shifting or curling happens during walking around. This is a huge pain because you need to pad the tape over the toes so you also don't do any damage to the scales of the foot. Tape your 2 outside toes down first and then loosely tape the broken toe down last. That way, the 2 intact toes bear the weight of the "cast" and the broken toe is just kept straight and protected from further injury. This really is a 2-person job to get it just right.
I hope this helps.
